Research ArticleEffect of Ta Additions on the MicrostructureDamping and Shape Memory Behaviour of PrealloyedCu-Al-Ni Shape Memory Alloys
Safaa N Saud1 E Hamzah2 H R Bakhsheshi-Rad3 and T Abubakar2
1Faculty of Information Science and Engineering Management and Science University 40100 Shah Alam Malaysia2Faculty of Mechanical Engineering Universiti Teknologi Malaysia 81310 UTM Johor Bahru Johor Malaysia3Advanced Materials Research Center Department of Materials Engineering Islamic Azad University Najafabad BranchNajafabad Iran
Correspondence should be addressed to E Hamzah esahfkmutmmy
Received 27 July 2016 Accepted 6 November 2016 Published 11 January 2017
Academic Editor Masamichi Yoshimura
Copyright copy 2017 Safaa N Saud et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The influence of Ta additions on themicrostructure and properties of Cu-Al-Ni shapememory alloys was investigated in this paperThe addition of Ta significantly affects the green and porosity densities the minimum percentage of porosity was observed with themodified prealloyed Cu-Al-Ni-20 wt Ta The phase transformation temperatures were shifted towards the highest values afterTa was added Based on the damping capacity results the alloy of Cu-Al-Ni-30 wt Ta has very high internal friction with themaximum equivalent internal friction value twice as high as that of the prealloyed Cu-Al-Ni SMA Moreover the prealloyed Cu-Al-Ni SMAs with the addition of 20 wt Ta exhibited the highest shape recovery ratio in the first cycle (ie 100 recovery) andwhen the number of cycles is increased this ratio tends to decrease On the other hand the modified alloys with 10 and 30 wt Taimplied a linear increment in the shape recovery ratio with increasing number of cycles Polarization tests in NaCl solution showedthat the corrosion resistance of Cu-Al-Ni-Ta SMA improved with escalating Ta concentration as shown by lower corrosion currentdensities higher corrosion potential and formation of stable passive film
1 Introduction
Cu-based shape memory alloys are being considered asa prospective material for applications including high-damping capacity material sensors and actuators Particu-larly Cu-Al-Ni alloys are revealed to be appropriate for high-temperature applications due to their high thermal stabilityat increased temperatures that is above 373K (100∘C) [1 2]In contrast the Cu-Al-Ni alloys produced by typical castingmethods had to endure the issue of critical brittleness as aresponse for large grain sizes (around several millimeters)together with large elastic anisotropy [3ndash5] For this reasona number of efforts have aimed to improve the ductilityof traditionally cast Cu-Al-Ni alloys via grain refining bythe addition of a fourth element which can include Ti ZrMn B Y V Co and rare earth metals [6ndash10] The grainsize of the resulting Cu-Al-Ni alloys was found to range
from approximately 100 to 800 120583m The grain refinementthroughout alloying additions displayed enhancement in themechanical properties of the Cu-Al-Ni alloys On the otherhand the alloying elements are convenient to burn (atmo-spheric melting) or perhaps evaporate (vacuum melting)while performing the melting process causing unrestrainedtransformation of temperature that can be significantly influ-enced by the composition of the alloy [11 12] As a result themechanical properties of such alloys remained unsatisfactoryfor most practical applications
Several investigations have aimed to develop fine-grainedCu-Al-Ni alloys with a grain size considerably less than100 120583m by using various powder metallurgy techniques [1314] These kinds of techniques depended on the Cu-Al-Nialloy powder whichwas prepared by either an inert gas atom-ization process or mechanical alloying of elemental powdersin a high-energy ball mill under inert gas atmosphere [15]
HindawiScanningVolume 2017 Article ID 1789454 13 pageshttpsdoiorg10115520171789454
2 Scanning
The mechanical alloying (MA) method [16 17] is one ofthe most desired methods it is indeed reported to bemore affordable and also convenient for manufacturingapplications MA is predominantly beneficial to synthesizealloys with significant variance in melting temperatures Themethod should prevent the mass loss of the componentwith the lower melting temperature due to the fact thatthe synthesis is performed near room temperature MA is apowder processing approach involving a sequence of repeatedwelds with fracturing of the powder particles inside a millFor the synthesis of prealloyed Cu-Al-Ni SMAs with freeporescracks numerous common sintering approaches havebeen studied [18ndash20] however most of these techniquesinvolve lengthy sintering times (gt3 h) and high sinteringtemperature (1050∘C) Hence there is strong interest fromthe PM industry to develop an innovative and superiorsintering process with finer microstructures and improvedphysical andmechanical propertiesThis is where microwavetechnology promises to be advantageous [21 22]
So far the addition of tantalum has shown a significanteffect on the microstructure mechanical properties andphase transformation temperature of shape memory alloys[23ndash25] due to its aptitude to reduce the transformationtemperature increase the thermal stability and improve thestrain recovery (120576reco) and residual strain (120576res) during thermalcycling Therefore it is suggested that Ta is a promising can-didate for the alloying element to improve the shape memoryproperty of SMAs [23] On the other hand the additionof Ta to Cu-Al-Ni SMAs has not been reported elsewheretherefore this research aims to investigate the influence ofdifferent amounts of Ta addition on phase transformationmechanical properties and corrosion behaviour of prealloyedpowders of Cu-Al-Ni SMAs
2 Experimental Procedure
21 Sample Preparation In this research the elemental pow-ders of Cu Al and Ni with Ta as an additional element wereprepared The specification of the elemental powder and theinitial powder mixture is shown in Table 1 These powdersof Cu-Al-Ni-119909Ta SMAs (119909 is 10 20 and 30 wt) wereprepared by mechanical alloying using planetary milling for1 h at 300 rpm For the mechanical alloying a Retsch PM100planetary ball mill with a zirconium oxide vial was used for1 h to confirm the homogeneity of the powder The rotationspeed of the ball mill was 300 rpm and ball to powder ratiowas approximately 5 1 by weight
The prealloyed powder was hot pressed into greensamples with dimensions of 12060115mm times (L) 10mm for themicrostructural characterization and 12060115mm times (L) 30mmfor the mechanical test through a 10-ton hand-operatedhydraulic press and a single-act piston die of 15mmdiameterwas utilized The compaction process was carried out at aconstant temperature of 300∘C for 10min the temperaturewas maintained via an external heater tape connected toa thermoset to maintain the exact temperature The greensamples were placed into a 245GHz 03ndash30 kW consistentlyflexible microwave device (HAMiLab-V3 SYNOTHERMCorp) The green samples were inserted inside an alumina
Table 1 Specification of elemental powders and mixture
sagger and covered with silicon carbide (SiC) The functionof SiC is usually to serve as a microwave susceptor toenable the heating system as well as sintering of the greensamples The samples were sintered by microwave heating ata rate of 20∘Cmin to 900∘C for 30min Argon gas with apurity of 99995 was pumped into the microwave chamberthroughout the sintering with the intent to protect againstoxidation Tomeasure the temperature of all samples throughthe sintering process a Raytek IR pyrometer was utilizedPrior to the microstructure characterization the sinteredsamples were homogenized at 900∘C for 30min and directlyquenched in water Homogenization of the Cu-Al-Ni alloysat temperatures in the 120573-phase field followed by rapid cool-ing produces microstructures formed by metastable phaseswhich can result in martensitic transformation
22 Porosity Calculation The green porosity was calculatedusing the following equation [26 27]
119875 = 1 minus ( 120588g120588th) times 100 (1)
where120588g is the green density and can be calculated by divisionof the calculated weight by the measured volume and 120588th isthe theoretical density of the samples and can be calculatedas follows [28]
120588th = [120588Cu0 times (at Cu) + 120588Al0 times (at Al) + 120588Ni0times (at Ni) + 120588Oxy0 times (at Oxy) + 120588additives0
times (at additives)] (2)
where 120588Cu0 120588Al0 120588Ni0 120588Oxy0 and 120588additives0 are the theoreticaldensities of the base-alloy elements and additives
23 Materials Characterization The microstructure changesof the prealloyed and homogenized samples were investigatedusing a field emission-scanning electron microscope (FE-SEM) Zeiss-LEO Model 1530 operated at 10 kV coupledwith energy-dispersive spectroscopy (EDS) operated at 10 kVThe results of EDS were indicated in accordance with astandardless semiquantitative analysis and an error bar invalue of 5 was added to each reading The phase andcrystal structure were identified using a D5000 Siemens X-ray diffractometer fitted with a Cu K120572 X-ray source witha locked coupled mode a 2120579 range between 30∘ and 80∘and a 005∘s scanning stepThe transformation temperaturesof the mechanically alloyed Cu-Al-Ni alloy specimens withand without addition were evaluated via differential scanningcalorimetry (DSC) at a heatingcooling rate of 10∘Cmin
Scanning 3
24 Mechanical Test The internal fractions of the Cu-Al-Nialloys with and without addition were evaluated by perform-ing the damping test on the specimens in themartensitic statewherein subsize test specimens with the dimension of 19mmtimes 3mm times 2mm were prepared The damping tests werecarried out in a DMA Q800 dynamic mechanical analyzerin single-cantilever mode at a constant vibration frequencyof 1Hz and displacement of 005mm with a temperaturerange from 20∘C to 300∘C and a constant heatingcoolingrate of 5∘Cmin To measure the shape memory recoveryof the prealloyed samples under multicycles isothermalcompressive loading and unloading were carried out at atested temperature of 200∘C and after each cycle the samplewas heated to 119879 gt 119860119891 that is asymp300∘C to obtain the shaperecovery
25 Corrosion Test For potentiodynamic polarization (PDP)tests cylindrical specimens with a surface area of 1 cm2 wereprepared PDP was carried out in an open-air glass cellcontaining 350mL of 3wt NaCl solution using a potentio-stat (PARSTAT 2263 Princeton Applied Research) A three-electrode cell was used for the PDP tests where a saturatedcalomel electrode (SCE) was used as the reference electrodea graphite rod as the counter electrode and an alloy specimenas the working electrode The samples were immersed in theSBF for 1 h prior to the PDP test to establish the open-circuitpotential The samples were immersed in the NaCl solutionfor 1 h prior to the PDP test to establish the open-circuitpotential All experiments (119899 = 3 where n indicates thenumber of replicates) were carried out in the range betweenminus250mV in the cathodic direction and+500mV in the anodicdirection relative to the open-circuit potential at a constantscan rate of 0167mVs The polarization resistance (119877119875) wascalculated according to the following equation [29 30]
where 119894corr is corrosion current density 120573119888 is cathodic Tafelslope and 120573119886 is anodic Tafel slope of the specimens The cor-rosion rate (119862119877) of the samples obtained from the corrosioncurrent density was calculated according to [31]
119862119877 = 2285119894corr (4)
Immersion testing was carried out according to ASTMG1-03Specimens with a diameter of 10mm and thickness of 10mmwere immersed in a beaker containing 200mL of 3wtNaClsolution for 30 days The immersion tests were repeated atleast once to verify the reproducibility of the results
3 Results and Discussion
31 Green Density and Porosity The variation of green den-sity and porosity of the modified and unmodified alloys as afunction of Ta amount is shown in Figures 1(a)ndash1(c) It can beclearly seen that the addition of Ta has produced a significanteffect on the porosity density in which the addition of20 wt Ta led to an increase in the green density from
5354 gcm3 to 6869 gcm3 in consequence of reducing thegreen porosity from 1296 to 75 On the other hand basedon the micrographs in Figure 1(a) it was found that the Cu-Al-Ni SMA contains some semimicron-sized pores and thatthese pores were distributed randomly in the microstructureThe area fractions of the pores were calculated using imageprocessing software known as 119894solution that also confirmedthe same trend of decrement with the addition of Ta in whichthe lowest area fraction of pores was observed with 20 wtTa addition With further increase in Ta amount to 30 wtthe area fraction of pores increased as shown in Figure 1(b)Utilizing 119894solution image processing software (119894solution DT)and in accordance with the ASTM E112-12 the grain sizesof the modified and unmodified prealloyed samples wereevaluated as indicated in Figure 1(c) It was observed that thegrain size of the modified prealloyed samples significantlydecreased and the smallest grain size was indicated withthe prealloyed sample of 20 wt Ta addition This kindof reduction is mainly related to the effect of mechanicalalloying which also suggested that approximately 2 at Tacan be forced into the Cu lattice to form a supersaturated Cu-rich solid solution [32 33] and produce a grain refinementDarling et al [32] have also revealed that the grain boundariesare more sensitive to the applied temperature of treatmentand diffusion rate of Ta phase In general the grain size ofCu-Al-Ni SMA which is produced by conventional castingwas determined to be 300ndash1400 120583m [34ndash36] even though thealloying elements and thermal treatments were applied
32 Microstructural Investigations Figures 2(a)ndash2(h) showmicrographs of prealloyed and homogenizedCu-Al-Ni SMAsassociated with the chemical analysis of the homogenisedsamples From the microstructure of prealloyed samples(see Figures 2(a)ndash2(d)) neck formation between the powderparticles can be easily seen these necks are caused by thecold working of the element powder that occurred duringthe mechanical alloying (ball-milling process) From the FE-SEM high-resolution images (Figures 2(e)ndash2(h)) it can beseen that there are two phases with different morphologiesplate-like and needle-like with a self-accommodating con-figuration inside the merged grains These phases are 12057310158401and 12057410158401 which are formed as thermally induced martensitesand varied in terms of thickness and orientation after theaddition of TaThe 12057410158401 phase formed as a coarse variantsplate-like phase while the 12057310158401 phase formed as a needle-likephase between the 12057410158401 phases The needle-like phase of 12057310158401martensite has a very pronounced thermoelastic behaviourwhich can be attributed to its controlled growth in the self-accommodating groups [37] However when Ta was addednew phases were formed and the volume fraction of theseprecipitates varied according to the amount of Ta added Itis well known that Ta is an attractive element that causes theformation of second-phaseintermetallic compounds afteraddition [25 38] On the other hand it was found thatthese precipitates were depleted in the AlNi matrix andhence the formation of12057310158401martensite is promoted [36]Theseprecipitates accommodate the 12057410158401 and 12057310158401 parent phases andtheir accommodation is in a coherent ormostly semicoherent
4 Scanning
Gre
en p
oros
ity (
)
52
54
56
58
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Ta concentration (wt)
5
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14
Gre
en d
ensit
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cm
3)
minus05 00 05 10 15 20 25 30 35
Green densityGreen porosity (isolution) Green porosity (formulation)
Figure 1 (a and b) Calculated green porosity and density of Cu-Al-Ni-xTa SMA using formulation and image process contrast (c) Grain sizemeasurement in accordance with ASTM E112-12
mode that depends on the precipitatesrsquo sizes and crystal-structure orientations relative to the parent phase [39]Therefore during the transformation of the precipitate intoa single martensite variant after being surrounded by matrixthe precipitate leaves its place as a vacancy However theoccurrence of an intrinsic deformation leads to a varietyof other precipitates that are severely deformed during thetransformation and thus the precipitate maintains its own
shape It is well known that the microstructure and hencethe mechanical behaviour of Cu-Al-Ni alloys change withthe alloy composition and the processing routes to whichthe samples are subjected The chemical compositions of theformed phasesprecipitates in Cu-Al-Ni-20 wt Ta alloyswere examined using EDS and are shown in Figure 2(i)It was found that the amount of elemental Ta in differentmicrostructural locations was significantly changed based on
Figure 2 Morphologies of the milled powder and homogenized Cu-Al-Ni SMAs with and without Ta addition ((a) and (e)) 0 wt Ta ((b)and (f)) 10 wt Ta ((c) and (g)) 20 wt Ta ((d) and (h)) 30 wt (i) EDS spectrums (j) XRD diffraction of Cu-Al-Ni-20 wt Ta SMAand (k) the magnified porosity with 30 wt Ta addition
the type of the formed phasesprecipitates Furthermore thepercentage of oxygenwas found to decrease after the additionof Ta and homogenization
The XRD patterns of the homogenized Cu-Al-Ni-119909TaSMAs with different percentages of Ta are presented inFigure 2(j) Indexing of these patterns shows that these only
consist of martensite phases 12057410158401 and 12057310158401 having a monoclinicstructure as main phases along with some other precip-itatesintermetallic compounds that are also formed afterbeing homogenized at 900∘C for 1 h After the addition of Tathe scannedpeaks changed in terms of 2120579 and intensity whichshows that theXRDpatterns ofCu-Al-Ni SMAare sensitive to
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
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120576rec ()72226110577852636667
(a)
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ss (M
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647577780909
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(b)
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ss (M
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1200
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120576rec120576p
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10082147435711165
120576rec ()
(c)
54321
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ss (M
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Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
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120576rec120576p120576r
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66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
The mechanical alloying (MA) method [16 17] is one ofthe most desired methods it is indeed reported to bemore affordable and also convenient for manufacturingapplications MA is predominantly beneficial to synthesizealloys with significant variance in melting temperatures Themethod should prevent the mass loss of the componentwith the lower melting temperature due to the fact thatthe synthesis is performed near room temperature MA is apowder processing approach involving a sequence of repeatedwelds with fracturing of the powder particles inside a millFor the synthesis of prealloyed Cu-Al-Ni SMAs with freeporescracks numerous common sintering approaches havebeen studied [18ndash20] however most of these techniquesinvolve lengthy sintering times (gt3 h) and high sinteringtemperature (1050∘C) Hence there is strong interest fromthe PM industry to develop an innovative and superiorsintering process with finer microstructures and improvedphysical andmechanical propertiesThis is where microwavetechnology promises to be advantageous [21 22]
So far the addition of tantalum has shown a significanteffect on the microstructure mechanical properties andphase transformation temperature of shape memory alloys[23ndash25] due to its aptitude to reduce the transformationtemperature increase the thermal stability and improve thestrain recovery (120576reco) and residual strain (120576res) during thermalcycling Therefore it is suggested that Ta is a promising can-didate for the alloying element to improve the shape memoryproperty of SMAs [23] On the other hand the additionof Ta to Cu-Al-Ni SMAs has not been reported elsewheretherefore this research aims to investigate the influence ofdifferent amounts of Ta addition on phase transformationmechanical properties and corrosion behaviour of prealloyedpowders of Cu-Al-Ni SMAs
2 Experimental Procedure
21 Sample Preparation In this research the elemental pow-ders of Cu Al and Ni with Ta as an additional element wereprepared The specification of the elemental powder and theinitial powder mixture is shown in Table 1 These powdersof Cu-Al-Ni-119909Ta SMAs (119909 is 10 20 and 30 wt) wereprepared by mechanical alloying using planetary milling for1 h at 300 rpm For the mechanical alloying a Retsch PM100planetary ball mill with a zirconium oxide vial was used for1 h to confirm the homogeneity of the powder The rotationspeed of the ball mill was 300 rpm and ball to powder ratiowas approximately 5 1 by weight
The prealloyed powder was hot pressed into greensamples with dimensions of 12060115mm times (L) 10mm for themicrostructural characterization and 12060115mm times (L) 30mmfor the mechanical test through a 10-ton hand-operatedhydraulic press and a single-act piston die of 15mmdiameterwas utilized The compaction process was carried out at aconstant temperature of 300∘C for 10min the temperaturewas maintained via an external heater tape connected toa thermoset to maintain the exact temperature The greensamples were placed into a 245GHz 03ndash30 kW consistentlyflexible microwave device (HAMiLab-V3 SYNOTHERMCorp) The green samples were inserted inside an alumina
Table 1 Specification of elemental powders and mixture
sagger and covered with silicon carbide (SiC) The functionof SiC is usually to serve as a microwave susceptor toenable the heating system as well as sintering of the greensamples The samples were sintered by microwave heating ata rate of 20∘Cmin to 900∘C for 30min Argon gas with apurity of 99995 was pumped into the microwave chamberthroughout the sintering with the intent to protect againstoxidation Tomeasure the temperature of all samples throughthe sintering process a Raytek IR pyrometer was utilizedPrior to the microstructure characterization the sinteredsamples were homogenized at 900∘C for 30min and directlyquenched in water Homogenization of the Cu-Al-Ni alloysat temperatures in the 120573-phase field followed by rapid cool-ing produces microstructures formed by metastable phaseswhich can result in martensitic transformation
22 Porosity Calculation The green porosity was calculatedusing the following equation [26 27]
119875 = 1 minus ( 120588g120588th) times 100 (1)
where120588g is the green density and can be calculated by divisionof the calculated weight by the measured volume and 120588th isthe theoretical density of the samples and can be calculatedas follows [28]
120588th = [120588Cu0 times (at Cu) + 120588Al0 times (at Al) + 120588Ni0times (at Ni) + 120588Oxy0 times (at Oxy) + 120588additives0
times (at additives)] (2)
where 120588Cu0 120588Al0 120588Ni0 120588Oxy0 and 120588additives0 are the theoreticaldensities of the base-alloy elements and additives
23 Materials Characterization The microstructure changesof the prealloyed and homogenized samples were investigatedusing a field emission-scanning electron microscope (FE-SEM) Zeiss-LEO Model 1530 operated at 10 kV coupledwith energy-dispersive spectroscopy (EDS) operated at 10 kVThe results of EDS were indicated in accordance with astandardless semiquantitative analysis and an error bar invalue of 5 was added to each reading The phase andcrystal structure were identified using a D5000 Siemens X-ray diffractometer fitted with a Cu K120572 X-ray source witha locked coupled mode a 2120579 range between 30∘ and 80∘and a 005∘s scanning stepThe transformation temperaturesof the mechanically alloyed Cu-Al-Ni alloy specimens withand without addition were evaluated via differential scanningcalorimetry (DSC) at a heatingcooling rate of 10∘Cmin
Scanning 3
24 Mechanical Test The internal fractions of the Cu-Al-Nialloys with and without addition were evaluated by perform-ing the damping test on the specimens in themartensitic statewherein subsize test specimens with the dimension of 19mmtimes 3mm times 2mm were prepared The damping tests werecarried out in a DMA Q800 dynamic mechanical analyzerin single-cantilever mode at a constant vibration frequencyof 1Hz and displacement of 005mm with a temperaturerange from 20∘C to 300∘C and a constant heatingcoolingrate of 5∘Cmin To measure the shape memory recoveryof the prealloyed samples under multicycles isothermalcompressive loading and unloading were carried out at atested temperature of 200∘C and after each cycle the samplewas heated to 119879 gt 119860119891 that is asymp300∘C to obtain the shaperecovery
25 Corrosion Test For potentiodynamic polarization (PDP)tests cylindrical specimens with a surface area of 1 cm2 wereprepared PDP was carried out in an open-air glass cellcontaining 350mL of 3wt NaCl solution using a potentio-stat (PARSTAT 2263 Princeton Applied Research) A three-electrode cell was used for the PDP tests where a saturatedcalomel electrode (SCE) was used as the reference electrodea graphite rod as the counter electrode and an alloy specimenas the working electrode The samples were immersed in theSBF for 1 h prior to the PDP test to establish the open-circuitpotential The samples were immersed in the NaCl solutionfor 1 h prior to the PDP test to establish the open-circuitpotential All experiments (119899 = 3 where n indicates thenumber of replicates) were carried out in the range betweenminus250mV in the cathodic direction and+500mV in the anodicdirection relative to the open-circuit potential at a constantscan rate of 0167mVs The polarization resistance (119877119875) wascalculated according to the following equation [29 30]
where 119894corr is corrosion current density 120573119888 is cathodic Tafelslope and 120573119886 is anodic Tafel slope of the specimens The cor-rosion rate (119862119877) of the samples obtained from the corrosioncurrent density was calculated according to [31]
119862119877 = 2285119894corr (4)
Immersion testing was carried out according to ASTMG1-03Specimens with a diameter of 10mm and thickness of 10mmwere immersed in a beaker containing 200mL of 3wtNaClsolution for 30 days The immersion tests were repeated atleast once to verify the reproducibility of the results
3 Results and Discussion
31 Green Density and Porosity The variation of green den-sity and porosity of the modified and unmodified alloys as afunction of Ta amount is shown in Figures 1(a)ndash1(c) It can beclearly seen that the addition of Ta has produced a significanteffect on the porosity density in which the addition of20 wt Ta led to an increase in the green density from
5354 gcm3 to 6869 gcm3 in consequence of reducing thegreen porosity from 1296 to 75 On the other hand basedon the micrographs in Figure 1(a) it was found that the Cu-Al-Ni SMA contains some semimicron-sized pores and thatthese pores were distributed randomly in the microstructureThe area fractions of the pores were calculated using imageprocessing software known as 119894solution that also confirmedthe same trend of decrement with the addition of Ta in whichthe lowest area fraction of pores was observed with 20 wtTa addition With further increase in Ta amount to 30 wtthe area fraction of pores increased as shown in Figure 1(b)Utilizing 119894solution image processing software (119894solution DT)and in accordance with the ASTM E112-12 the grain sizesof the modified and unmodified prealloyed samples wereevaluated as indicated in Figure 1(c) It was observed that thegrain size of the modified prealloyed samples significantlydecreased and the smallest grain size was indicated withthe prealloyed sample of 20 wt Ta addition This kindof reduction is mainly related to the effect of mechanicalalloying which also suggested that approximately 2 at Tacan be forced into the Cu lattice to form a supersaturated Cu-rich solid solution [32 33] and produce a grain refinementDarling et al [32] have also revealed that the grain boundariesare more sensitive to the applied temperature of treatmentand diffusion rate of Ta phase In general the grain size ofCu-Al-Ni SMA which is produced by conventional castingwas determined to be 300ndash1400 120583m [34ndash36] even though thealloying elements and thermal treatments were applied
32 Microstructural Investigations Figures 2(a)ndash2(h) showmicrographs of prealloyed and homogenizedCu-Al-Ni SMAsassociated with the chemical analysis of the homogenisedsamples From the microstructure of prealloyed samples(see Figures 2(a)ndash2(d)) neck formation between the powderparticles can be easily seen these necks are caused by thecold working of the element powder that occurred duringthe mechanical alloying (ball-milling process) From the FE-SEM high-resolution images (Figures 2(e)ndash2(h)) it can beseen that there are two phases with different morphologiesplate-like and needle-like with a self-accommodating con-figuration inside the merged grains These phases are 12057310158401and 12057410158401 which are formed as thermally induced martensitesand varied in terms of thickness and orientation after theaddition of TaThe 12057410158401 phase formed as a coarse variantsplate-like phase while the 12057310158401 phase formed as a needle-likephase between the 12057410158401 phases The needle-like phase of 12057310158401martensite has a very pronounced thermoelastic behaviourwhich can be attributed to its controlled growth in the self-accommodating groups [37] However when Ta was addednew phases were formed and the volume fraction of theseprecipitates varied according to the amount of Ta added Itis well known that Ta is an attractive element that causes theformation of second-phaseintermetallic compounds afteraddition [25 38] On the other hand it was found thatthese precipitates were depleted in the AlNi matrix andhence the formation of12057310158401martensite is promoted [36]Theseprecipitates accommodate the 12057410158401 and 12057310158401 parent phases andtheir accommodation is in a coherent ormostly semicoherent
4 Scanning
Gre
en p
oros
ity (
)
52
54
56
58
60
62
64
66
68
70
72
Ta concentration (wt)
5
6
7
8
9
10
11
12
13
14
Gre
en d
ensit
y (g
cm
3)
minus05 00 05 10 15 20 25 30 35
Green densityGreen porosity (isolution) Green porosity (formulation)
Figure 1 (a and b) Calculated green porosity and density of Cu-Al-Ni-xTa SMA using formulation and image process contrast (c) Grain sizemeasurement in accordance with ASTM E112-12
mode that depends on the precipitatesrsquo sizes and crystal-structure orientations relative to the parent phase [39]Therefore during the transformation of the precipitate intoa single martensite variant after being surrounded by matrixthe precipitate leaves its place as a vacancy However theoccurrence of an intrinsic deformation leads to a varietyof other precipitates that are severely deformed during thetransformation and thus the precipitate maintains its own
shape It is well known that the microstructure and hencethe mechanical behaviour of Cu-Al-Ni alloys change withthe alloy composition and the processing routes to whichthe samples are subjected The chemical compositions of theformed phasesprecipitates in Cu-Al-Ni-20 wt Ta alloyswere examined using EDS and are shown in Figure 2(i)It was found that the amount of elemental Ta in differentmicrostructural locations was significantly changed based on
Figure 2 Morphologies of the milled powder and homogenized Cu-Al-Ni SMAs with and without Ta addition ((a) and (e)) 0 wt Ta ((b)and (f)) 10 wt Ta ((c) and (g)) 20 wt Ta ((d) and (h)) 30 wt (i) EDS spectrums (j) XRD diffraction of Cu-Al-Ni-20 wt Ta SMAand (k) the magnified porosity with 30 wt Ta addition
the type of the formed phasesprecipitates Furthermore thepercentage of oxygenwas found to decrease after the additionof Ta and homogenization
The XRD patterns of the homogenized Cu-Al-Ni-119909TaSMAs with different percentages of Ta are presented inFigure 2(j) Indexing of these patterns shows that these only
consist of martensite phases 12057410158401 and 12057310158401 having a monoclinicstructure as main phases along with some other precip-itatesintermetallic compounds that are also formed afterbeing homogenized at 900∘C for 1 h After the addition of Tathe scannedpeaks changed in terms of 2120579 and intensity whichshows that theXRDpatterns ofCu-Al-Ni SMAare sensitive to
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
24 Mechanical Test The internal fractions of the Cu-Al-Nialloys with and without addition were evaluated by perform-ing the damping test on the specimens in themartensitic statewherein subsize test specimens with the dimension of 19mmtimes 3mm times 2mm were prepared The damping tests werecarried out in a DMA Q800 dynamic mechanical analyzerin single-cantilever mode at a constant vibration frequencyof 1Hz and displacement of 005mm with a temperaturerange from 20∘C to 300∘C and a constant heatingcoolingrate of 5∘Cmin To measure the shape memory recoveryof the prealloyed samples under multicycles isothermalcompressive loading and unloading were carried out at atested temperature of 200∘C and after each cycle the samplewas heated to 119879 gt 119860119891 that is asymp300∘C to obtain the shaperecovery
25 Corrosion Test For potentiodynamic polarization (PDP)tests cylindrical specimens with a surface area of 1 cm2 wereprepared PDP was carried out in an open-air glass cellcontaining 350mL of 3wt NaCl solution using a potentio-stat (PARSTAT 2263 Princeton Applied Research) A three-electrode cell was used for the PDP tests where a saturatedcalomel electrode (SCE) was used as the reference electrodea graphite rod as the counter electrode and an alloy specimenas the working electrode The samples were immersed in theSBF for 1 h prior to the PDP test to establish the open-circuitpotential The samples were immersed in the NaCl solutionfor 1 h prior to the PDP test to establish the open-circuitpotential All experiments (119899 = 3 where n indicates thenumber of replicates) were carried out in the range betweenminus250mV in the cathodic direction and+500mV in the anodicdirection relative to the open-circuit potential at a constantscan rate of 0167mVs The polarization resistance (119877119875) wascalculated according to the following equation [29 30]
where 119894corr is corrosion current density 120573119888 is cathodic Tafelslope and 120573119886 is anodic Tafel slope of the specimens The cor-rosion rate (119862119877) of the samples obtained from the corrosioncurrent density was calculated according to [31]
119862119877 = 2285119894corr (4)
Immersion testing was carried out according to ASTMG1-03Specimens with a diameter of 10mm and thickness of 10mmwere immersed in a beaker containing 200mL of 3wtNaClsolution for 30 days The immersion tests were repeated atleast once to verify the reproducibility of the results
3 Results and Discussion
31 Green Density and Porosity The variation of green den-sity and porosity of the modified and unmodified alloys as afunction of Ta amount is shown in Figures 1(a)ndash1(c) It can beclearly seen that the addition of Ta has produced a significanteffect on the porosity density in which the addition of20 wt Ta led to an increase in the green density from
5354 gcm3 to 6869 gcm3 in consequence of reducing thegreen porosity from 1296 to 75 On the other hand basedon the micrographs in Figure 1(a) it was found that the Cu-Al-Ni SMA contains some semimicron-sized pores and thatthese pores were distributed randomly in the microstructureThe area fractions of the pores were calculated using imageprocessing software known as 119894solution that also confirmedthe same trend of decrement with the addition of Ta in whichthe lowest area fraction of pores was observed with 20 wtTa addition With further increase in Ta amount to 30 wtthe area fraction of pores increased as shown in Figure 1(b)Utilizing 119894solution image processing software (119894solution DT)and in accordance with the ASTM E112-12 the grain sizesof the modified and unmodified prealloyed samples wereevaluated as indicated in Figure 1(c) It was observed that thegrain size of the modified prealloyed samples significantlydecreased and the smallest grain size was indicated withthe prealloyed sample of 20 wt Ta addition This kindof reduction is mainly related to the effect of mechanicalalloying which also suggested that approximately 2 at Tacan be forced into the Cu lattice to form a supersaturated Cu-rich solid solution [32 33] and produce a grain refinementDarling et al [32] have also revealed that the grain boundariesare more sensitive to the applied temperature of treatmentand diffusion rate of Ta phase In general the grain size ofCu-Al-Ni SMA which is produced by conventional castingwas determined to be 300ndash1400 120583m [34ndash36] even though thealloying elements and thermal treatments were applied
32 Microstructural Investigations Figures 2(a)ndash2(h) showmicrographs of prealloyed and homogenizedCu-Al-Ni SMAsassociated with the chemical analysis of the homogenisedsamples From the microstructure of prealloyed samples(see Figures 2(a)ndash2(d)) neck formation between the powderparticles can be easily seen these necks are caused by thecold working of the element powder that occurred duringthe mechanical alloying (ball-milling process) From the FE-SEM high-resolution images (Figures 2(e)ndash2(h)) it can beseen that there are two phases with different morphologiesplate-like and needle-like with a self-accommodating con-figuration inside the merged grains These phases are 12057310158401and 12057410158401 which are formed as thermally induced martensitesand varied in terms of thickness and orientation after theaddition of TaThe 12057410158401 phase formed as a coarse variantsplate-like phase while the 12057310158401 phase formed as a needle-likephase between the 12057410158401 phases The needle-like phase of 12057310158401martensite has a very pronounced thermoelastic behaviourwhich can be attributed to its controlled growth in the self-accommodating groups [37] However when Ta was addednew phases were formed and the volume fraction of theseprecipitates varied according to the amount of Ta added Itis well known that Ta is an attractive element that causes theformation of second-phaseintermetallic compounds afteraddition [25 38] On the other hand it was found thatthese precipitates were depleted in the AlNi matrix andhence the formation of12057310158401martensite is promoted [36]Theseprecipitates accommodate the 12057410158401 and 12057310158401 parent phases andtheir accommodation is in a coherent ormostly semicoherent
4 Scanning
Gre
en p
oros
ity (
)
52
54
56
58
60
62
64
66
68
70
72
Ta concentration (wt)
5
6
7
8
9
10
11
12
13
14
Gre
en d
ensit
y (g
cm
3)
minus05 00 05 10 15 20 25 30 35
Green densityGreen porosity (isolution) Green porosity (formulation)
Figure 1 (a and b) Calculated green porosity and density of Cu-Al-Ni-xTa SMA using formulation and image process contrast (c) Grain sizemeasurement in accordance with ASTM E112-12
mode that depends on the precipitatesrsquo sizes and crystal-structure orientations relative to the parent phase [39]Therefore during the transformation of the precipitate intoa single martensite variant after being surrounded by matrixthe precipitate leaves its place as a vacancy However theoccurrence of an intrinsic deformation leads to a varietyof other precipitates that are severely deformed during thetransformation and thus the precipitate maintains its own
shape It is well known that the microstructure and hencethe mechanical behaviour of Cu-Al-Ni alloys change withthe alloy composition and the processing routes to whichthe samples are subjected The chemical compositions of theformed phasesprecipitates in Cu-Al-Ni-20 wt Ta alloyswere examined using EDS and are shown in Figure 2(i)It was found that the amount of elemental Ta in differentmicrostructural locations was significantly changed based on
Figure 2 Morphologies of the milled powder and homogenized Cu-Al-Ni SMAs with and without Ta addition ((a) and (e)) 0 wt Ta ((b)and (f)) 10 wt Ta ((c) and (g)) 20 wt Ta ((d) and (h)) 30 wt (i) EDS spectrums (j) XRD diffraction of Cu-Al-Ni-20 wt Ta SMAand (k) the magnified porosity with 30 wt Ta addition
the type of the formed phasesprecipitates Furthermore thepercentage of oxygenwas found to decrease after the additionof Ta and homogenization
The XRD patterns of the homogenized Cu-Al-Ni-119909TaSMAs with different percentages of Ta are presented inFigure 2(j) Indexing of these patterns shows that these only
consist of martensite phases 12057410158401 and 12057310158401 having a monoclinicstructure as main phases along with some other precip-itatesintermetallic compounds that are also formed afterbeing homogenized at 900∘C for 1 h After the addition of Tathe scannedpeaks changed in terms of 2120579 and intensity whichshows that theXRDpatterns ofCu-Al-Ni SMAare sensitive to
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
Figure 1 (a and b) Calculated green porosity and density of Cu-Al-Ni-xTa SMA using formulation and image process contrast (c) Grain sizemeasurement in accordance with ASTM E112-12
mode that depends on the precipitatesrsquo sizes and crystal-structure orientations relative to the parent phase [39]Therefore during the transformation of the precipitate intoa single martensite variant after being surrounded by matrixthe precipitate leaves its place as a vacancy However theoccurrence of an intrinsic deformation leads to a varietyof other precipitates that are severely deformed during thetransformation and thus the precipitate maintains its own
shape It is well known that the microstructure and hencethe mechanical behaviour of Cu-Al-Ni alloys change withthe alloy composition and the processing routes to whichthe samples are subjected The chemical compositions of theformed phasesprecipitates in Cu-Al-Ni-20 wt Ta alloyswere examined using EDS and are shown in Figure 2(i)It was found that the amount of elemental Ta in differentmicrostructural locations was significantly changed based on
Figure 2 Morphologies of the milled powder and homogenized Cu-Al-Ni SMAs with and without Ta addition ((a) and (e)) 0 wt Ta ((b)and (f)) 10 wt Ta ((c) and (g)) 20 wt Ta ((d) and (h)) 30 wt (i) EDS spectrums (j) XRD diffraction of Cu-Al-Ni-20 wt Ta SMAand (k) the magnified porosity with 30 wt Ta addition
the type of the formed phasesprecipitates Furthermore thepercentage of oxygenwas found to decrease after the additionof Ta and homogenization
The XRD patterns of the homogenized Cu-Al-Ni-119909TaSMAs with different percentages of Ta are presented inFigure 2(j) Indexing of these patterns shows that these only
consist of martensite phases 12057410158401 and 12057310158401 having a monoclinicstructure as main phases along with some other precip-itatesintermetallic compounds that are also formed afterbeing homogenized at 900∘C for 1 h After the addition of Tathe scannedpeaks changed in terms of 2120579 and intensity whichshows that theXRDpatterns ofCu-Al-Ni SMAare sensitive to
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
Figure 2 Morphologies of the milled powder and homogenized Cu-Al-Ni SMAs with and without Ta addition ((a) and (e)) 0 wt Ta ((b)and (f)) 10 wt Ta ((c) and (g)) 20 wt Ta ((d) and (h)) 30 wt (i) EDS spectrums (j) XRD diffraction of Cu-Al-Ni-20 wt Ta SMAand (k) the magnified porosity with 30 wt Ta addition
the type of the formed phasesprecipitates Furthermore thepercentage of oxygenwas found to decrease after the additionof Ta and homogenization
The XRD patterns of the homogenized Cu-Al-Ni-119909TaSMAs with different percentages of Ta are presented inFigure 2(j) Indexing of these patterns shows that these only
consist of martensite phases 12057410158401 and 12057310158401 having a monoclinicstructure as main phases along with some other precip-itatesintermetallic compounds that are also formed afterbeing homogenized at 900∘C for 1 h After the addition of Tathe scannedpeaks changed in terms of 2120579 and intensity whichshows that theXRDpatterns ofCu-Al-Ni SMAare sensitive to
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
Figure 2 Morphologies of the milled powder and homogenized Cu-Al-Ni SMAs with and without Ta addition ((a) and (e)) 0 wt Ta ((b)and (f)) 10 wt Ta ((c) and (g)) 20 wt Ta ((d) and (h)) 30 wt (i) EDS spectrums (j) XRD diffraction of Cu-Al-Ni-20 wt Ta SMAand (k) the magnified porosity with 30 wt Ta addition
the type of the formed phasesprecipitates Furthermore thepercentage of oxygenwas found to decrease after the additionof Ta and homogenization
The XRD patterns of the homogenized Cu-Al-Ni-119909TaSMAs with different percentages of Ta are presented inFigure 2(j) Indexing of these patterns shows that these only
consist of martensite phases 12057410158401 and 12057310158401 having a monoclinicstructure as main phases along with some other precip-itatesintermetallic compounds that are also formed afterbeing homogenized at 900∘C for 1 h After the addition of Tathe scannedpeaks changed in terms of 2120579 and intensity whichshows that theXRDpatterns ofCu-Al-Ni SMAare sensitive to
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
Cu-Al-Ni 207 235 226 19625Cu-Al-Ni-10 wt Ta 2258 26757 263 2118Cu-Al-Ni-20 wt Ta 2427 2774 2656 2379Cu-Al-Ni-30 wt Ta 2405 2656 2568 229
the amount of added Ta On the other hand thematrix of Cu-Al-Ni SMA as the predominant phase was always retainedeven though Ta amounts varied
33 Transformation Temperatures The endothermic andexothermic curves of the prealloyed samples of Cu-Al-Niwith and without Ta addition are shown in Figure 3 and thedetermined data are tabulated in Table 2 The endothermiccurve during the heating represented the transformationof martensite to austenite phase and this transformationis represented by the transformation temperatures of 119860 119904and 119860119891 austenite start and finish respectively Meanwhilethe exothermic curve during the cooling represented thetransformation of austenite to martensite phase which isrepresented by the transformation temperatures of 119872119904 and119872119891 martensite start and finish respectively From Figure 3it can be seen that the forward and backward transformationsshow one-step transformation in the modified and unmod-ified prealloyed samples due to the existence of a smoothsingle peak The result reveals that the transformation tem-peratures are shifted towards higher temperatures When theamount of Ta was approximately 10 wt the transformationtemperatures were slightly increased Further increasing theamount of Ta to 20 wt the transformation temperatureswere rapidly increased compared with the unmodified alloy
Cu-Al-NiCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Temperature (∘C)
025
0225
02
0175
015
0125
01
0075
00525 50 75 100 125 150 175 200 225 250 275 300
Tan 120575
Figure 4 Internal friction heating curves of Cu-Al-Ni-xTa SMAs
However the addition of 30 wt Ta led to decreasing thetransformation temperatures compared with 20 Ta sampleIt is well known that the transformation temperatures aremainly affected by the presence of precipitates porosity andtheir volume fraction [35 40 41] Based on the micrographsin Figures 1(a) and 1(b) it is apparent that the percentage ofporosity was increased as the percentage of Ta increased to20 and 30 wt and thus the transformation temperaturesdecreased
34 Mechanical Properties
341 Damping In order to obtain the most accurate damp-ing behaviour of the materials Tan 120575 is the most suitablemeasurement as it can give the ideal evolution of the signalover time Within the low frequency the peak of Tan 120575during the martensitic transformation is mainly attributedto the transient internal friction [42 43] When the alloy isset at a certain temperature in an isothermal condition thevalue of Tan 120575 is significantly decreased which is associatedwith delaying the inherent internal friction and the intrinsicinternal friction Figure 4 shows the internal friction (Tan 120575)against the applied temperature in which based on Tan 120575curve there is only one peak observed for the modified andunmodified alloys which is related to the phase transitionIt was found that the addition of Ta has significantly variedin the value of Tan 120575 obtaining the highest value with theaddition of 30 wt of Ta with respect to the base alloyIt can be also seen that the relaxation peak increased withincreasing Ta amount This is evidently explained by thepresence of a multitude of Ta precipitates which interferewith the movement of dislocations in the martensite phaseand constitute the primary reason for the relaxation event
In order to determine the influence of porosity on thedamping behaviour and based on previous studies [44 45]an effective parameter namely equivalent internal friction
8 Scanning
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
(119876minus1eqv) was proposed and the value of this parameter can bedetermined using the following formula
119876minus1eqv = 119876minus1(1 minus 119875) (5)
where 119876minus1 is the internal friction and 119875 is the porosity Theresults show that the equivalent internal friction was found tobe in the consequence of 30 wt Ta gt 20 wt Ta gt 10 wtTa gt 0wt Ta in which the modified alloy with 30 wt Tahas highest119876minus1eqv which is almost twice that of the unmodifiedalloy The mechanisms of internal friction for the Cu-Al-NiSMAs are mainly related to the martensitic interfaces andtransformation behaviour During the mechanical loadingand unloading and the thermal process the martensite harraustenite phase transformation exhibits a dramatic lattice-softening phenomenon and twin boundaries in the austenitephase are easier to form than in themartensite which resultedin a higher damping capacity
On the other hand the presence of porosity may leadto making a difference in the elastic modulus and thermalexpansion with respect to the matrix and thus cause a highthermal stress concentration around the pores [46] In otherwords that causes the pores to have a very complicated andinhomogeneous stress-strain state inwhich this state causes adilatation and distortion of pores and hereafter the dilatationand distortion energy increasedThedilatation and distortionof pores incorporate a number of processes including disloca-tionmotion and formationwhich is certainly initialized in thematerial to relax stress concentration and then contributesto the dissipation of the elastic energy [47] It is usuallyapparent that when the damping derives from a dislocationmechanism it can be explained by strain amplitude reliance[48] In addition the martensitic transformation is alsocontrolled slightly within the presence of porosity in SMAsand the index of energy dissipation and therefore the valueof Tan 120575 declines with increasing the density of porosityand decreasing of the grain size [47] This statement canbe supported by the lower number of IF values for theunmodified alloy that has the highest density of porosity asindicated in Figures 1(a) and 1(b)
342 Shape Memory Characteristics Figures 5(a)ndash5(d) showthe stress-strain curves measured for each training cycle ofthe modified and unmodified prealloyed Cu-Al-Ni SMAsThe stress is plotted against the prestrain that performed at atemperature of 200∘C and the indicated arrows within 119909-axisrepresent the strain recovery by shape memory effect at thecorresponding cycle that was measured at a temperature of300∘C In accordancewith the s-s curves it was found that thecompressive stress increased after the addition of Ta whichhas increased almost fourfold compared with the unmodifiedalloys On the other hand the shape memory recovery wasalso enhanced after the addition of Ta The highest shapememory recovery was indicated with the modified alloy of20 wt Ta (Figure 5(c)) which shows almost 100 recoveryafter being heated above 119860119891 (ie 300∘C) at the first cyclehowever as a further number of cycles were performedthis ratio tended to decrease Both alloys of 10 wt and
30 wt show a linear increment in the strain recovery withincreasing number of cycles as observed in Figures 5(b) and5(d) The fluctuations in the residual strain and recoverystrain are mainly dependent on the direction and movementof martensite interfaces and dislocations [49 50] When themultitraining cycles were performed the martensite variantswere oriented unidirectionally and therefore the plasticstrain was stored in the samples Within a certain number ofcycles the local stress is formed and results in increases in thedensity of dislocation and imperfections which in oppositecauses interlocking the dislocations and thus suppressingthe movement of the martensite variants As a result thephase is unable to transform to the martensite phase andmore residual plastic deformation is stored in the sample[51 52] On the other hand increasing the number of thermalloading and unloading cycles can also result in increasesin the volume fraction of the martensite variants As aconsequence the structure of dislocations and martensiticvariants remained constant during the training cycles andtherefore the shape memory effect decreased As furthernumbers of training cycles are increased associated withinducing a certain stress at a specific position the density ofdislocation reached the saturation level and led to the shapememory characteristics being stabilized
35 Electrochemical and Immersion Test Typical potentiody-namic polarization curves of base Cu-Al-Ni SMA and Cu-Al-Ni-119909Ta (119909 = 10 20 and 30 wt) SMAs are plottedin Figure 6 Corrosion potential (119864corr) corrosion currentdensity (119894corr) and polarization resistance (119877119875) of the SMAsamples are presented in Table 3 119864corr of SMA contain-ing Ta was nobler compared with the base SMA sample119864corr of the Cu-Al-Ni-10 wt Ta sample was approximatelyminus2205mVSCE whereas that of the base SMA sample wasaround minus2616mVSCE The Cu-Al-Ni-30 wt Ta sampleevidently had more positive 119864corr (minus1593mVSCE) comparedwith the Cu-Al-Ni-20 wt Ta sample (minus1851mVSCE) Thisillustrated that the addition of Ta to the base SMA sam-ple ennobles the open-circuit potential In fact the SMAcontaining 30 wt Ta indicates the nobler pitting potentialthat causes a decline of pitting susceptibility and increasespitting corrosion resistance [53] Polarization curves alsodisplay that 119894corr of the base SMA and Cu-Al-Ni-10 wtTa SMA was 1176 and 784120583A cmminus2 respectively The baseSMA is not passivated and dissolves actively forming acorrosion product film [54] Thus the Cu-Al-Ni-10 wtTa SMA presented better corrosion resistance than that ofthe base SMA Addition of 20 and 30 wt Ta to the baseSMA reduced 119894corr to 327 and 128 120583A cmminus2 respectively Thehigher corrosion resistance of the SMA containing higher Taconcentration is due to the rapid formation of a passive filmwith a highly protective quality and high uniformity [54]
From the curve it can be observed that 120573119886 is sim007Vdecade for the SMA containing Ta This value is close tothe theoretical and experimental value of 006Vdecade forcopper in chloride media at room temperature [55] 119877119901values indicated a positive influence of Ta additions on thecorrosion behaviour of Cu-Al-Ni SMA alloy Thus 119877119901 values
Scanning 9
54321
Stre
ss (M
Pa)
Strain ()
450
400
350
300
250
200
150
100
50
00 05 1 15 2 25 3 35 4 45 5 55 6 65
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
120576rec ()72226110577852636667
(a)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
647577780909
120576rec ()
(b)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
1400
1300
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p
120576r
Cycle12345
10082147435711165
120576rec ()
(c)
54321
Stre
ss (M
Pa)
Strain ()0 05 1 15 2 25 3 35 4 45 5 55 6
1000
900
800
700
600
500
400
300
200
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
120576rec120576p120576r
Cycle12345
66678076793684
7857
120576rec ()
(d)
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
Figure 5 Stress-strain curves of Cu-Al-Ni-xTa SMAs loaded and unloaded at 200∘C and then preheated to 300∘C (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt
Table 3 Electrochemical parameters of ternary Cu-Al-Ni and quaternary Cu-Al-Ni-Ta SMAs in 3wt NaCl solution obtained from thepolarization test
AlloyCorrosion potential119864corr (mV versus
SCE)
Current density119894corr (120583Acm2)
Cathodic slope120573119862 (mVdecade)
versus SCE
Anodic slope120573119886
(mVdecade)versus SCE
Polarization resistance119877119875 (kΩcm2)
Corrosion rate119862119877 (mmyear)
CuminusAlminusNi minus2616 1176 minus211 78 457 268CuminusAlminusNiminus10 Ta minus2205 784 minus184 76 718 179CuminusAlminusNiminus20 Ta minus1851 327 minus148 72 1864 074CuminusAlminusNiminus30 Ta minus1593 128 minus220 69 3414 029
10 Scanning
Base alloyCu-Al-Ni-10wt Ta
Cu-Al-Ni-20wt TaCu-Al-Ni-30wt Ta
Current density (Acmminus2)
02
01
0
minus01
minus02
minus03
minus04
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
minus051E minus 08 1E minus 06 1E minus 04 1E minus 02 0
Pote
ntia
l(V
SCE)
Figure 6 Potentiodynamic polarization curves of specimens in3wt NaCl solution (a) black curve Cu-Al-Ni and Cu-Al-Ni-TaSMAs with various Ta content (b) red curve 10 (c) blue curve 20and (d) green curve 30 wt
increased from 457 to 718 KΩ cm2 when a small quantity ofTa (10 wt) was added to the base SMA Further additionof 20ndash30 wt Ta to the base SMA leads to a significantincrease of 119877119901 value in the range of 1864ndash3414 KΩ cm2 Thisindicated that the addition of 30 wt Ta to base SMA ledto the formation of a highly protective passive film even inaggressive chloride-containing solution [54] In this regardtantalum-containing alloys showed high corrosion resistancedue to spontaneous passivation in aggressive media [56]Tantalum addition to base SMA leads to a decreasing trend incorrosion rate (119862119877) particularly when 30 wtTawas added119862119877 values shown in Table 3 clearly indicate the corrosionrate in the following order Cu-Al-Ni Cu-Al-Ni-10 Ta Cu-Al-Ni-20 Ta and Cu-Al-Ni-30 Ta The lowest corrosion rateof Cu-Al-Ni-30 Ta SMA is attributed to the presence of ahigh concentration of Ta ions in the corrosion product filmwhich has low solubility in aggressive chloride-containingsolution [54] In view of this it was reported that tantalumis an essential element to improve the corrosion resistanceof SMA in aggressive media [56] Surface morphologiesof the Cu-Al-Ni and Cu-Al-Ni-119909Ta SMA after 30 days ofimmersion in NaCl solution are shown in Figure 7 Base Cu-Al-Ni SMA indicated small pits and a significant amount ofsurface cracking on the surface of the base SMA which isdue to dehydration after removal from theNaCl solutionThebase alloy dissolves actively owing to the formation of theCuCl2
minus complex anion [53] From Figure 7(b) the presenceof pitting and corrosion products can be observed on thesurface of Cu-Al-Ni-10 Ta SMA However lower amountsof corrosion products were detected after the addition of20 wt Ta to the base SMA (Figure 7(c)) SMA contain-ing 30 wt Ta yielded the formation of dense uniformprotective films enriched in tantalum ions that cover theentire SMA surface (Figure 7(d)) [57] A plateau in the
anodic polarization curve can clearly be seen revealing theformation of passive film on the 30 wt Ta SMA surface[57] However Cu-Al-Ni and Cu-Al-Ni-10 Ta SMAs werenot passivated and dissolved actively indicating that the 20ndash30 wt Ta addition to the base SMA stabilizes the protectivefilm This suggests the presence of tantalum in a corrosionproduct such as tantalum oxyhydroxide film functioning asthe effective barrier film El-Moneim [57] showed that thepresence of tantalum in single solid solution phase alloyssuppresses the active dissolution process and enhances theprotective quality of the passive film formed EDS analysis(Point 1) shows high amounts of Cu Cl and O accompaniedby low content of Ni indicating the formation of coppercompounds in the form of oxide or chloride and aluminumoxide The presence of Ta (Point 2) further confirmed thattantalum is concentrated in the passive film In this regardBadawy et al [58] reported that in the corrosion productin ternary aluminum-containing copper alloys composedof two layers the under layer is Cu2O Al2O3 sdot 119909H2Othe overlayer is a mixture of Al2O3 and Cu2O HoweverMontecinos and Simison [59] suggested that the corrosionproduct of the Cu-Al-Be SMA in chloridemedia is composedof Al2O3sdotH2O Cu2O CuO (CuCO3sdotCu(OH)2) and CuCl2In view of this the formation of protective tantalum-enrichedfilm in addition to Al-dihydroxychloride Cu-oxides andCu-chlorides is responsible for the high corrosion resistance ofCu-Al-Ni-Ta SMA
4 Conclusions
TheCu-Al-Ni alloy as a potential type of shape memory alloywas successfully produced by powdermetallurgy mechanicalalloying andmicrowave sinteringThe addition effects of dif-ferent amounts of Ta on the microstructure transformationtemperature damping capacity shape memory effect andcorrosion behaviour were systematically investigated and themain conclusions are as follows
(1) After the microwave sintering at 900∘C the Ta parti-cles were uniformly distributed in the matrix of Cu-Al-Ni and different types of precipitates were formedin the binding domain between the Ta and AlNiphase
(2) The porosity density and grain size were reduced afterthe addition of Ta inwhich the smallest grain size andlowest porosity were observed in prealloyedCu-Al-Niafter being modified with 20 wt Ta
(3) The highest transformation temperatures and strainrecovery by shape memory effect were indicated inprealloyed Cu-Al-Ni-20 wt Ta while the highestinternal friction was present in the prealloyed Cu-Al-Ni-30 wt TaThese variations aremainly attributedto the density of porosity grain refinement and pres-ence of precipitates whereas these parameters signif-icantly control the movement of martensite interfacesand dislocations thus controlling the mechanicalproperties
(4) The electrochemical corrosion performance of theCu-Al-Ni-Ta SMA was enhanced via increasing the
Scanning 11
A
B
(a) (b)
(c) (d)
1 2 3 4 5
Al
Cl ClCl
Cl
C C
O Ni
Cu Al
TaTa
O
Ni
Cu
1 2 3 4 5
10120583m5120583m
10120583m10120583m
Point A Point B
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
Figure 7 SEM micrographs of (a) Cu-Al-Ni and Cu-Al-Ni-xTa SMAs with various Ta content (b) 10 (c) 20 and (d) 30 wt andcorresponding EDS analyses of points A and B after immersion into 3wt NaCl for 30 days
Ta concentration The result also indicated that amore stable passive oxide film containing tantalumoxyhydroxide formed on the surface of Cu-Al-Ni-30Ta SMA which resulted in better corrosion resistancecompared with the other SMAs
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
The authors would like to thank the Ministry of HigherEducation of Malaysia and Universiti Teknologi Malaysia
for providing the financial support under the UniversityResearch Grant no QJ130000302400M57 and researchfacilities
References
[1] Z C Lin W Yu R H Zee and B A Chin ldquoCuAlPd alloys forsensor and actuator applicationsrdquo Intermetallics vol 8 no 5-6pp 605ndash611 2000
[2] J Font E Cesari J Muntasell and J Pons ldquoThermomechanicalcycling in Cu-Al-Ni-based melt-spun shape-memory ribbonsrdquoMaterials Science and Engineering A vol 354 no 1-2 pp 207ndash211 2003
[3] T Tadaki K Otsuka and C M Wayman ldquoShape memorymaterialsrdquo Cu-based shape memory alloys pp 97ndash116 1998
12 Scanning
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
[4] S Miyazaki K Otsuka H Sakamoto and K Shimizu ldquoThefracture of CundashAlndashNi shape memory alloyrdquo Transactions of theJapan Institute of Metals vol 22 no 4 pp 244ndash252 1981
[5] S W Husain and P C Clapp ldquoThe intergranular embrittlementof Cu-AI-Ni 120573-phase alloysrdquo Journal of Materials Science vol22 no 7 pp 2351ndash2356 1987
[6] S N Saud T A Abu Bakar E Hamzah M K Ibrahim andA Bahador ldquoEffect of quarterly element addition of cobalton phase transformation characteristics of Cu-Al-Ni shapememory alloysrdquoMetallurgical andMaterials TransactionsA vol46 no 8 pp 3528ndash3542 2015
[7] S N Saud E Hamzah T Abubakar M K Ibrahim and ABahador ldquoEffect of a fourth alloying element on themicrostruc-ture and mechanical properties of CundashAlndashNi shape memoryalloysrdquo Journal of Materials Research vol 30 no 14 pp 2258ndash2269 2015
[8] S N Saud E Hamzah T Abubakar andH R Bakhsheshi-RadldquoCorrelation ofmicrostructural and corrosion characteristics ofquaternary shape memory alloys Cu-Al-Ni-X (X=Mn or Ti)rdquoTransactions of Nonferrous Metals Society of China vol 25 no4 Article ID 63711 pp 1158ndash1170 2015
[9] M AMorris ldquoMicrostructural influence on ductility and shapememory effect of some modified Cu-Ni-Al alloysrdquo ScriptaMetallurgica et Materiala vol 25 no 6 pp 1409ndash1414 1991
[10] Y Gao M Zhu and J K L Lai ldquoMicrostructure characteri-zation and effect of thermal cycling and ageing on vanadium-doped CundashAlndashNindashMn high-temperature shape memory alloyrdquoJournal of Materials Science vol 33 no 14 pp 3579ndash3584 1998
[11] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoDependence of the martensitic transformationcharacteristics on concentration in CundashAlndashNi shape memoryalloysrdquo Materials Science and Engineering A vol 273ndash275 pp380ndash384 1999
[12] V Recarte R B Perez-Saez E H Bocanegra M L No andJ San Juan ldquoInfluence of Al and Ni concentration on themartensitic transformation in Cu-Al-Ni shape-memory alloysrdquoMetallurgical and Materials Transactions A vol 33 no 8 pp2581ndash2591 2002
[13] S K Vajpai R K Dube and S Sangal ldquoMicrostructure andproperties of Cu-Al-Ni shape memory alloy strips prepared viahot densification rolling of argon atomized powder preformsrdquoMaterials Science and Engineering A vol 529 no 1 pp 378ndash3872011
[14] G Lojen I Anzel A Kneissl et al ldquoMicrostructure of rapidlysolidified CundashAlndashNi shape memory alloy ribbonsrdquo Journal ofMaterials Processing Technology vol 162-163 pp 220ndash229 2005
[15] S K Vajpai R K Dube and S Sangal ldquoProcessing and char-acterization of Cu-Al-Ni shape memory alloy strips preparedfrom prealloyed powder by hot densification rolling of powderpreformsrdquoMetallurgical and Materials Transactions A PhysicalMetallurgy and Materials Science vol 42 no 10 pp 3178ndash31892011
[16] C SuryanarayanaNon-Equilibrium Processing of Materials vol2 Elsevier 1999
[17] M F Giordana M R Esquivel and E Zelaya ldquoA detailedstudy of phase evolution in Cuminus16 at Al and Cuminus30 at Alalloys under different types of mechanical alloying processesrdquoAdvanced Powder Technology vol 26 no 2 pp 470ndash477 2015
[18] B Y Li L J Rong Y Y Li and V E Gjunter ldquoSynthesis ofporous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis reaction mechanism and anisotropy in
pore structurerdquo Acta Materialia vol 48 no 15 pp 3895ndash39042000
[19] Y Zhao M Taya Y Kang and A Kawasaki ldquoCompressionbehavior of porous NiTi shape memory alloyrdquo Acta Materialiavol 53 no 2 pp 337ndash343 2005
[20] B Yuan X P Zhang C Y Chung M Q Zeng and MZhu ldquoA comparative study of the porous TiNi shape-memoryalloys fabricated by three different processesrdquoMetallurgical andMaterials Transactions A vol 37 no 3 pp 755ndash761 2006
[21] F Kongoli ldquoSohn International Symposium on lsquoadvanced pro-cessing of metals and materialsrsquordquo Transactions of the Institutionsof Mining and Metallurgy vol 117 no 2 pp 65ndash66 2008
[22] M Oghbaei and O Mirzaee ldquoMicrowave versus conventionalsintering a review of fundamentals advantages and applica-tionsrdquo Journal of Alloys and Compounds vol 494 no 1-2 pp175ndash189 2010
[23] H Y Kim S Hashimoto J I Kim T Inamura H Hosoda andS Miyazaki ldquoEffect of Ta addition on shape memory behaviorof Tindash22Nb alloyrdquoMaterials Science and Engineering A vol 417no 1-2 pp 120ndash128 2006
[24] J Liu H X Zheng M X Xia and J G Li ldquoThe microstructureand martensitic transformation of CondashNindashGandashTa ferromag-netic shape memory alloysrdquo Scripta Materialia vol 52 no 10pp 955ndash958 2005
[25] WY PengNWYangG LQuWWWangH P Shi andW JWang ldquoEffect of ta addition on properties and microstructuresof Fe-28Ni-115Al shape memory alloysrdquo Materials ScienceForum vol 787 pp 288ndash294 2014
[26] X Rao C L Chu and Y Y Zheng ldquoPhase compositionmicrostructure and mechanical properties of porous TindashNbndashZr alloys prepared by a two-step foaming powder metallurgymethodrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 34 pp 27ndash36 2014
[27] Y-W Kim K-C Choi Y-S Chung E Choi and T-H NamldquoMicrostructure andmartensitic transformation characteristicsof gas-atomized Ti-Ni-Cu powdersrdquo Journal of Alloys andCompounds vol 577 supplement 1 pp S227ndashS231 2013
[28] A S Jabur J T Al-Haidary and E S Al-Hasani ldquoCharac-terization of Ni-Ti shape memory alloys prepared by powdermetallurgyrdquo Journal of Alloys and Compounds vol 578 pp 136ndash142 2013
[29] G R Argade K Kandasamy S K Panigrahi and R S MishraldquoCorrosion behavior of a friction stir processed rare-earthaddedmagnesium alloyrdquoCorrosion Science vol 58 pp 321ndash3262012
[30] H R Bakhsheshi-Rad M R Abdul-Kadir M H Idris and SFarahany ldquoRelationship between the corrosion behavior andthe thermal characteristics and microstructure of Mgndash05CandashxZn alloysrdquo Corrosion Science vol 64 pp 184ndash197 2012
[31] Z Shi M Liu and A Atrens ldquoMeasurement of the corrosionrate of magnesium alloys using Tafel extrapolationrdquo CorrosionScience vol 52 no 2 pp 579ndash588 2010
[32] K A Darling A J Roberts Y Mishin S N Mathaudhu and LJ Kecskes ldquoGrain size stabilization of nanocrystalline copper athigh temperatures by alloying with tantalumrdquo Journal of Alloysand Compounds vol 573 pp 142ndash150 2013
[33] P C Millett R P Selvam and A Saxena ldquoStabilizing nanocrys-talline materials with dopantsrdquo Acta Materialia vol 55 no 7pp 2329ndash2336 2007
[34] S N Saud E Hamzah T Abubakar H R Bakhsheshi-RadM Zamri and M Tanemura ldquoEffects of Mn additions on the
Scanning 13
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
structuremechanical properties and corrosion behavior of Cu-Al-Ni shape memory alloysrdquo Journal of Materials Engineeringand Performance vol 23 no 10 pp 3620ndash3629 2014
[35] S N Saud E Hamzah T Abubakar M Zamri and MTanemura ldquoInfluence of Ti additions on the martensitic phasetransformation and mechanical properties of Cu-Al-Ni shapememory alloysrdquo Journal of Thermal Analysis and Calorimetryvol 118 no 1 pp 111ndash122 2014
[36] V Sampath ldquoStudies on the effect of grain refinement andthermal processing on shape memory characteristics of Cu-Al-Ni alloysrdquo Smart Materials and Structures vol 14 no 5 ppS253ndashS260 2005
[37] Y Aydogdu A Aydogdu and O Adiguzel ldquoSelf-accommodating martensite plate variants in shape memoryCuAlNi alloysrdquo Journal of Materials Processing Technology vol123 no 3 pp 498ndash500 2002
[38] C Booth-Morrison R D Noebe and D N Seidman ldquoEffectsof a tantalum addition on themorphological and compositionalevolution of a model Ni-Al-Cr superalloyrdquo in Proceedings of the11th International Symposium on Superalloys (SuperAlloys rsquo08)pp 73ndash79 Champion Pa USA September 2008
[39] F C Lovey and E Cesari ldquoOn the microstructural character-istics of non-equilibrium 120574 precipitates in Cu-Zn-Al alloysrdquoMaterials Science and Engineering A vol 129 no 1 pp 127ndash1331990
[40] M Zarinejad Y Liu and Y Tong ldquoTransformation temperaturechanges due to second phase precipitation in NiTi-based shapememory alloysrdquo Intermetallics vol 17 no 11 pp 914ndash919 2009
[41] B Yuan X P Zhang C Y Chung and M Zhu ldquoThe effectof porosity on phase transformation behavior of porous Ti-508 at Ni shape memory alloys prepared by capsule-free hotisostatic pressingrdquo Materials Science and Engineering A vol438-440 pp 585ndash588 2006
[42] A Nespoli E Villa and F Passaretti ldquoEffect of Yttrium onmicrostructure thermal properties and damping capacity ofNi41Ti50Cu9 alloyrdquo Journal of Alloys and Compounds vol 653pp 234ndash242 2015
[43] K-N Lin and S-K Wu ldquoMulti-stage transformation inannealed Ni-rich Ti49Ni41Cu10 shape memory alloyrdquo Inter-metallics vol 18 no 1 pp 87ndash91 2010
[44] Y-P Zhang and X-P Zhang ldquoInternal friction behaviors ofporous NiTi alloys with variable porositiesrdquo Chinese Journal ofNonferrous Metals vol 19 no 10 pp 1872ndash1879 2009
[45] H-J Jiang C-B Ke S-S Cao X Ma and X-P ZhangldquoPhase transformation and damping behavior of lightweightporous TiNiCu alloys fabricated by powdermetallurgy processrdquoTransactions of Nonferrous Metals Society of China (EnglishEdition) vol 23 no 7 pp 2029ndash2036 2013
[46] Q Wang C Cui N Yan and F Han ldquoInternal friction peaksin a porous CuAlMn shape memory alloyrdquo Advanced MaterialsResearch vol 479-481 pp 1303ndash1306 2012
[47] Q Wang F Han J Wu and G Hao ldquoDamping behavior ofporous CuAlMn shape memory alloyrdquoMaterials Letters vol 61no 11-12 pp 2598ndash2600 2007
[48] A S Nowick Anelastic Relaxation in Crystalline Solids vol 1Elsevier Amsterdam Netherlands 2012
[49] U Sari and I Aksoy ldquoMicro-structural analysis of self-accommodating martensites in Cundash1192 wt Alndash378 wt Nishapememory alloyrdquo Journal ofMaterials Processing Technologyvol 195 no 1-3 pp 72ndash76 2008
[50] J Dutkiewicz ldquoSuperelasticity and shape memory effect incopper base alloysrdquo Acta Physica Polonica A vol 96 no 2 pp197ndash212 1999
[51] X L Meng Y F Zheng Z Wang and L C Zhao ldquoShapememory properties of the Ti36Ni49Hf15 high temperature shapememory alloyrdquo Materials Letters vol 45 no 2 pp 128ndash1322000
[52] Q M Nafari and S M Abbasi ldquoInfluence of compositionand thermomechanical training process on the transformationbehavior and shape memory properties of NiTi based alloysrdquoTransactions of the Indian Institute of Metals vol 66 no 3 pp239ndash245 2013
[53] C Qin W Zhang K Asami N Ohtsu and A Inoue ldquoGlassformation corrosion behavior and mechanical properties ofbulk glassy Cu-Hf-Ti-Nb alloysrdquoActaMaterialia vol 53 no 14pp 3903ndash3911 2005
[54] H-J Lee E Akiyama H Habazaki A Kawashima K Asamiand K Hashimoto ldquoThe roles of tantalum and phosphorus inthe corrosion behavior ofNi-Ta-P alloys in 12MHClrdquoCorrosionScience vol 39 no 2 pp 321ndash332 1997
[55] S Montecinos and S Simison ldquoCorrosion behavior of Cu-Al-Be shape memory alloys with different compositions andmicrostructuresrdquo Corrosion Science vol 74 pp 387ndash395 2013
[56] J Bhattarai E Akiyama H Habazaki A Kawashima KAsami andKHashimoto ldquoThe passivation behavior of sputter-deposited W-Ta alloys in 12 M HClrdquo Corrosion Science vol 40no 4-5 pp 757ndash779 1998
[57] A A El-Moneim E Akiyama H Habazaki A Kawashima KAsami and K Hashimoto ldquoThe corrosion behaviour of sputter-deposited amorphous Mn-Ta alloys in 05M NaCl solutionrdquoCorrosion Science vol 39 no 10-11 pp 1965ndash1979 1997
[58] W A Badawy M M El-Rabiei and H Nady ldquoSynergisticeffects of alloying elements in Cu-ternary alloys in chloridesolutionsrdquo Electrochimica Acta vol 120 pp 39ndash45 2014
[59] S Montecinos and S N Simison ldquoInfluence of the microstruc-ture on the corrosion behaviour of a shape memory Cu-Al-Bealloy in amarine environmentrdquoApplied Surface Science vol 257no 7 pp 2737ndash2744 2011
