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Erosion behaviour of a Ti3SiC2 cathode under low-current vacuum arc
View the table of contents for this issue, or go to the journal homepage for more
IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS
J. Phys. D: Appl. Phys. 46 (2013) 395202 (8pp) doi:10.1088/0022-3727/46/39/395202
Erosion behaviour of a Ti3SiC2 cathodeunder low-current vacuum arcPeng Zhang, Tungwai L Ngai, Heng Xie and Yuanyuan Li
National Engineering Research Center of Near-net-shape Forming Technology for Metallic Materials,School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou510640, People’s Republic of China
Received 20 June 2013, in final form 14 August 2013Published 13 September 2013Online at stacks.iop.org/JPhysD/46/395202
AbstractIn this article, the arc erosion behaviour of high-purity Ti3SiC2 in vacuum was investigated byx-ray diffraction, scanning electron microscope, energy dispersive x-ray spectroscopy, andmicro-Raman spectroscopy. From the results obtained, Ti3SiC2 is unstable due to the highenergy intensity and high temperature of the vacuum arc. The dissociation of Ti3SiC2 takesplace at the sample surface, resulting in the formation of solid TiCx and gaseous Si. TiCx isejected from cathode to the surface of anode while Si is evaporated to the vacuum chamber.The micro-Raman results reveal that small amounts of carbon appeared as a by-product of thedissociation of Ti3SiC2, indicating that the Ti–C bonding is broken down under the vacuum arc.
(Some figures may appear in colour only in the online journal)
1. Introduction
In the 1960s, the ternary compound Ti3SiC2 was firstsynthesized via chemical reaction by Jeitschko et al [1].Ti3SiC2 has a hexagonal crystal structure with a space groupof P 63/mmc, which can be described as two edge-shared Ti6Coctahedron layers linked together by a two-dimensional closedpacked Si layer [1, 2].
Extensive investigations of this ternary compound havebeen carried out due to its combination of exceptionalproperties of both metals and ceramics [3–9]. The reportedelectrical conductivity of Ti3SiC2 is greater than the value oftitanium metal at room-temperature [3, 4, 6]. It is announcedthat the good electrical conductivity is related to the crystalchemistry of Ti3SiC2, for which the Ti6C octahedra in Ti3SiC2
exhibit a distortion of −2.87% with respect to those in TiC[3]. The high-temperature chemical stability of Ti3SiC2
has been explored in many works as well, but the resultsare quite conflicting. For example, El-Raghy and Barsoum[5] stated Ti3SiC2 is thermally stable at temperatures ashigh as 1700 ◦C. From the report of Low [7], however, thedecomposition of Ti3SiC2 commences at 1200 ◦C and becomespronounced at 1600 ◦C. Ti3SiC2 also shows a relatively highthermal conductivity, a reasonably low coefficient of thermalexpansion, damage tolerant, and resistant to thermal shock[4, 6, 8]. Besides, Ti3SiC2 possesses attractive properties such
as high oxidation [7] and chemical resistance, excellent high-temperature strength [6], self-lubrication [4], low frictioncoefficient [9], good machinability [6], high-temperatureplasticity [6] and so on [4, 6, 7, 9].
The performance of a vacuum interrupter depends to alarge extent on the characteristics of the contact materialsplaced into its vacuum chamber. Contact materials are thekey prerequisite to conduct electricity and heat, to interrupthigh-current, to keep away from welding, to withstand severearc erosion, and so on. However, it is really hard to find amaterial to satisfy all of the major requirements at the sametime. The known contact materials are usually developed bycombining two or more components to mutually compensateeach other and meet specific applications. On account of theexclusive mechanical and physical properties of Ti3SiC2, high-temperature stability, high electrical conductivity etc, it has thepotential to be the candidate for electric contact materials forvacuum interrupter. In this article, we try to investigate theerosion behaviour of Ti3SiC2 and verify its chemical stabilityunder the vacuum arc.
2. Experimental details
Commercially available Ti, Si and graphite powders were usedto synthesize Ti3SiC2. The powders were mixed accordingto a molar ratio of 3Ti : 1.1Si : 2C, the powders were vacuum
J. Phys. D: Appl. Phys. 46 (2013) 395202 P Zhang et al
Table 1. The cathodes and anodes arrangement of the experiments.
I II III
Cathode Ti3SiC2 (C1) Ti3SiC2 (C100) Ti3SiC2 (Cm)Anode Mo (A1) Ti3SiC2(A100) Mo (Am)Breakdown times 1 100 100
dried and then cold-pressed into a green body at 100 MPa, andthen sintering at 1500 ◦C for 2 h in a vacuum furnace. Theverified high-purity Ti3SiC2 (by x-ray diffractometry, usingCu Kα radiation) was crushed and ground into powders again.The powders were compacted into a graphite mould (20 mm indiameter) and sintered in vacuum (1 × 10−4 Pa) at 1500 ◦C byusing spark plasma sintering (SPS) technique. The heatingrate was 50 ◦C min−1, the soaking time was 5 min and theapplied pressure was maintained constant at 50 MPa duringsintering. The density of the sintered samples was measuredby Archimedes method.
After polishing, the sample was cleaned in acetone toremove surface grease and then rinsed with deionized water,followed by drying in a vacuum oven at 70 ◦C for 15 min.The samples were put in a sample holder, which was madeof copper. The cathodes were Ti3SiC2 and the anodes wereMo or Ti3SiC2 (see table 1) depending on the purpose of thestudy. The discharge gap distance between the two electrodeswas fixed at 0.3 mm. The vacuum breakdown was tested in achamber with a diameter of 30 cm and a height of 40 cm. Thechamber was filled with argon and evacuated to 1×10−4 Pa by amechanical pump and a sputter ion pump. The arcs were fed bya modified electric welder which applied a 10 kV dc voltage tothe gap between cathode and anode. The peak arc current wasabout 20 A and the arc time was set to 0.2 s. The arc current,arcing time and arc voltage of the discharge were recorded bya Tektronix TDS-210 digital memory oscilloscope.
The microstructures and composition of the treatedsamples were investigated by a scanning electron telescope(JXA-8100) equipped with energy dispersive x-ray (EDX)spectroscopy. Raman spectra were recorded with amicro-optical spectrometer system (LabRam Aramis Ramanspectrometer) equipped with a CCD detector and threedifferent laser wavelength sources at 532.8, 633 and 785 nm.The as-prepared and the treated samples were characterized byx-ray diffraction (XRD) with a Cu Kα source.
3. Result
3.1. XRD
In figure 1, XRD patterns of the samples which experienceddifferent times of vacuum arcs are presented. Figure 1(a)shows the x-ray profiles of the Ti3SiC2 cathodes in experimentI and II, respectively. As revealed from profile C1 (Ti3SiC2
cathode after first vacuum breakdown), excepting those peaksfor main phase Ti3SiC2, weak peaks corresponding to TiCx
phase were also detected in this sample. Increasing the timesof vacuum breakdown to 100, the profile (see C100) shows amore intense TiCx signal, while the intensity of Ti3SiC2 peaksdecreases. No peak of Si, C or Ti–Si intermetallics, which may
be derived from the dissociation of Ti3SiC2, was found in theprofile. Figure 1(b) shows the XRD profile of the Mo anode(experiment III) after 100 times of vacuum breakdown. Apartfrom those peaks of Mo, weak peaks corresponding to TiCx arealso observed, from which we conclude that the decompositionof Ti3SiC2 cathode results in the formation of TiCx , wheresome of the TiCx ejects to the opposite electrode.
3.2. Scanning electron microscope and EDX
Figure 2 shows the surface morphologies of sample C1 after thefirst vacuum breakdown. As shown in figure 2(a), the erosionarea is uniformly distributed over the entire surface of thecathode. There are less distinct erosion craters in this samplecomparing with those of alloys [10] and composites [11, 12].Figure 2(b) exhibits representative morphology of the centralerosion regions of sample C1, where the craters are distributedmore homogeneously and the crater depths are flatter thanthose from eroded alloys [10] and composites [11, 12]. Asdenoted by the arrows, the arrangement of the craters (about20 µm in size) indicates the random motion of the cathodespot from one position to another. The erosion pits presentedon the edge region of the erosion area (see figure 2(c)),which have a size of several micrometres, show a very similarerosion pattern to that appearing on Cu and Cr phases [10].Figure 2(d) is a magnified image of figure 2(b). Comparingwith Cu–Cr alloys [10] and metal based composite [11, 12],the erosion area of pure Ti3SiC2 is flatter, with network-likecracks dispersed on the entire erosion region. It is believedthat the presence of cracks on the surface have something todo with the thermal stress caused by the discharge process.The interaction between the cathode spot and the material willgive rise to high-temperature corrosion on the cathode surface.The following accumulation of thermal stress will result in thepresence of cracks in those regions.
After first discharge, the distribution of the elements on thecathode surface revealed by EDX analysis is shown in table 2.The atomic proportions of Ti and Si in zones B, C, and D areapproximately 3 : 1, corresponding to the Ti3SiC2 phase. Thechemistry of zone A, however, with an atomic ratio about 4 : 1,indicates phase transition occurring under the impact of thecathode spots.
An overview of the surface condition of sample C100 after100 times discharges is shown in figure 3(a). Many protrusionswith dimension from hundreds of micrometres down to tens ofmicrometres are observed on the surface. Figure 3(b) showsan enlarged micrograph of figure 3(a). As indicated by thearrows, many cavities were found accompanied by network-like cracks. The formation of cavities can be interpreted asfollows: with densely distributed pores and defects, the grainboundaries of polycrystalline Ti3SiC2 are very vulnerable tothe influences of the cathode spots; as impacted by the cathodespot, the grain boundaries experience strong local heating,decomposition, evaporation and explosive ejection, resultingin the formation of caves as shown in the picture. Figure 3(c)shows the surface of the Ti3SiC2-anode of experiment II. Itappears that the anode is inert, with many granular depositswhich came from the opposite direction presented on the
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Figure 1. XRD patterns for (a) Ti3SiC2 cathode after 1 and 100 times of breakdown; (b) Mo anode after 100 times of breakdown.
Figure 2. Scanning electron microscope (SEM) micrographs of Ti3SiC2 after first vacuum breakdown: (a) an overview of the erosionregions; arc erosion pattern in (b) central zone and (c) edge; (d) is an amplified image of (b).
Table 2. EDX analysis of selected zones as shown in figures 2–4, in at%.
J. Phys. D: Appl. Phys. 46 (2013) 395202 P Zhang et al
Figure 3. SEM micrographs of Ti3SiC2 surface after 100 times of vacuum breakdown; (a) Ti3SiC2 cathode; (b) is an amplified image of (a);(c) Ti3SiC2-anode; (d) is an amplified image of (c).
surface. A logical explanation is that, as a result of the lowarc current (20 A) in this experiment, the anode acted only asa collector of the flux ejected from the cathode. Figure 3(d)is a magnified photograph of the granular deposits shown infigure 3(c). From this photograph, the granules clearly consistof even smaller particles.
The chemical composition of the selected locations onsample C100 and sample A100 are shown in table 2. It shouldbe mentioned that the Ti : Si atomic ratio of the selected zonesof C100 (E–G) is distributed in a range of 3–4. At zone I, withthe Si content declined to 3.99%, the Ti : C ratio indicated theformation of TiCx phase. The data in table 2 (E–J) corroboratesthe fact that the Ti : Si atomic ratio of sample A100 is higherthan that of sample C100. In comparison with the chemicalcomposition of the cathode surface, the anode surface containsnoticeably less Si content. One explanation for this is that theanode acts only as a collector of the cathode ejections in low-current arcs. Due to the high temperature of the arcs, thedissociation of Ti3SiC2 cathode and the evaporation of Si tookplace during the ejection and deposition processes.
Figure 4 shows the surface morphology of Mo anodeof experiment III, with a Ti3SiC2 cathode and dischargingfor 100 times. Figure 4(a) is a low magnification scanningelectron microscope (SEM) (back- scattered electron) image.
The Mo surface is covered by deposits having two kinds ofstructures, granular-like and block-like. The granular depositsare very similar to those spherical graphite droplets observedon graphite electrodes under vacuum arc discharges [13].Much block-like debris with a size larger than 100 µm can befound. From a magnified image of figure 4(b), the granulardeposits consist of many even smaller droplets, which areidentical to those observed on the surface of A100 (as shown infigures 3(c) and (d)). From a magnified image (see figure 4(c)),coarse T-shape debris can be seen above the granular deposits.
For the metal cathode, investigations have shown that themass lost basically comprised three components: ions, neutralvapour and macro-particles. Macro-particles are usuallydroplets or solid debris generated during the plasma formationprocess. Ions and particles are two dominant forms of thecathode mass loss, and vapour losses are considered to be low[14, 15]. For the deposits as shown in figure 4, we can concludethat the granular deposits were formed by the deposition ofions, neutral vapour and droplets. However, for the block-likedebris observed in the photographs, they are bigger than thecathode craters (shown in figure 2). It is concluded that theycome from the fracture of protrusions on the cathode surface(as shown in figure 2).
EDX analysis was carried out again to identify thechemical composition of the deposits. The results revealed that
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J. Phys. D: Appl. Phys. 46 (2013) 395202 P Zhang et al
Figure 4. Surface morphology of Mo anode after 100 times of vacuum breakdown, (b) and (c) are amplified images of (a).
only a low amount of Si (no more than 5 at%) residues remainedon the surface of the Mo anode. Though the EDX techniquehas difficulty in quantitative analysis of C element, the atomicproportion of Ti and C indicated the formation of TiCx phase.These results agree well with the XRD analysis in figure 1(b)that TiCx is the major product of the decomposition of Ti3SiC2.From both EDX and XRD results, it is reasonable to concludethat Si was released from the electrodes in the gaseous form.During the arc discharge process, intense heating and strongforces will act on the cathode surface. The drastic interactionbetween the cathode spot and the cathode materials will resultin the formation of the cathode craters and the phase transitionof the cathode material [15, 16].
3.3. Micro-Raman
The Raman spectra of a Ti3SiC2single crystal showed fourpeaks at 224 cm−1, 278 cm−1, 625 cm−1 and 673 cm−1, whichare assigned to the E2g , A1g , E2g , and A1g modes, respectively[17]. For the polycrystalline Ti3SiC2, the spectrum exhibitedsix sharp peaks at 159, 228, 281, 312, 631 and 678 cm−1 anda wide peak centred at 372 cm−1 [18]. In our experiment(see lower line in figure 5(b)), the SPSed Ti3SiC2 sampledetected three sharp peaks at 216, 620 and 672 cm−1, inaddition to a broad peak centred at 280 cm−1. Micro-Raman
spectra measured on three different points of the fringe zoneof arc-eroded area (cathode C1) after the first breakdown,as shown in figure 5(a). Points A and B are located atinner and outer of a molten pool in the impacted area, andpoint C is close to the impacted area. The spectra showtwo broad peaks at around 255 and 603 cm−1 and also weakpeaks at approximately 360 and 660 cm−1. These peaksare comparable with the non-stoichiometric TiCx reportedby [18, 19]. It should be noticed that stoichiometric TiChas no Raman active modes and the observed modes inTiCx are disorder-induced Raman scattering due to carbonvacancies.
From the Raman spectrum of D point (figure 5(b)), thechemical information of the molten pool on the Ti3SiC2
cathode (C100) is revealed. There are two wide peaks atapproximately 255 and 603 cm−1, which correspond to thedisorder-induced Raman peaks of TiCx [18, 19].
As shown in figure 5(c), spectrum E showed the chemicalinformation of the T-shape block on the Mo anode (Am)
surface. The spectrum shows four peaks centred around 268,354, 524 and 603 cm−1. As mentioned above, peaks at around268, 354 and 603 cm−1 are derived from disorder-inducedRaman modes of TiCx . The peak observed at 524 cm−1
cannot be assigned at present. The chemical information ofthe granules on the Mo surface is also achieved as shown in
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Figure 5. Raman spectra analysis of selected locations on: (a) the fringe zone of arc eroded C1; (b) the molten pool of the C100,self-prepared polycrystalline Ti3SiC2; (c) the deposits on the Mo-anode surface.
spectrum F. The spectrum shows two strong broadening peaksat approximately 1338 and 1559 cm−1, which are assigned tothe D band (disordered band) and G band (graphite band) ofcarbon, respectively. Weak peaks at around 367 and 604 cm−1
indicate that a small amount of TiCx had formed.
4. Discussion
At moderate current (<10 kA) oxidized or contaminatedelectrode surface contribute significant effects on cathodespots. On a contaminated surface, the craters are smaller
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and separated from each other. Whereas on a clean surface(metallic surface with a few monolayer of adsorbed gas), thecraters form an overlapping chain. If we use the conceptintroduced in the Handbook of Vacuum Arc Science andTechnology [20], the appearance of the cathode craters inthis study (see figure 2) is connected with the formation oftype 1 spots, suggesting that the contamination on the electrodesurface altered the cathode spots behaviour. However,considering the good anti-oxidation resistance of Ti3SiC2 andthe cleaning of the samples by acetone, the chance of serioussurface contamination is low. The reason for the cathodecraters being subjected to type 1 spots is that the cathodematerial is a ceramic itself, in many aspects it behaves likeoxides more than metals.
In experiment I, by combining the XRD and micro-Ramanresults, it is demonstrated that the decomposition of Ti3SiC2
happened on the C1 surface, and the main product is TiCx .While the EDX results give the chemical compositions whichcorrespond to the Ti3SiC2 phase. In experiment II, accordingto the XRD analysis, the increase of the TiCx peak intensityas well as the decrease of Ti3SiC2 intensity is observed on theC100, indicating the severe decomposition of Ti3SiC2 phase.The micro-Raman analysis of the molten pool also confirmsthe formation of TiCx in those areas (see figure 5(b)). TheEDX analyses reveal that some zones of the C100 surface havea Ti : Si atomic ratio larger than 3, confirming the dissociationof Ti3SiC2. The EDX results are in accordance with the micro-Raman and XRD results in this experiment. For sample Am
of experiment III, by analysing the deposit on the Mo-anodesurface, the XRD pattern reveals the presence of TiCx whichis the product of the arc erosion. However, no signal of Si wasdetected. This result further confirms that the dissociation ofTi3SiC2 took place during the vacuum breakdown process. Thechemical compositions of the granular deposits obtained bymeans of EDX technique, however, show a small quantity of Sicontent (below 5 at%). From the block-like debris, the Ramanpeaks of TiCx are detected. From the granular deposits, twostrong Raman peaks of carbon and several weak peaks assignedto TiCx are observed. Since Raman spectrum is particularlysusceptible to the microstructure of the carbon, two unusuallystrong bands of carbon are exhibited in figure 5(c), indicatingthe generation of elemental carbon during the electrical arcdischarge.
The presence of deviation between EDX and micro-Raman results may be owing to the different workingmechanisms of these two devices: the EDX technique is usedto characterize the elemental composition, while the Ramanspectrum reveals the vibrational states of a molecule whichdepend on the electronic structure and the inter-atomic forcesof the molecule. We believe that Raman spectroscopy is a moreappropriate method to characterize carbides.
The temperature of the cathode spot is very high (usuallymore than several thousands of degrees), which is sufficientto cause the dissociation of Ti3SiC2. It is believed that theevaporation of Si took place and Ti3SiC2 decomposed to TiCx
during the electric arc discharge. Small amounts of carbonmay appear as a by-product of the dissociation of Ti3SiC2
due to the high energy intensity and high temperature of thevacuum arcs.
The dissociation of Ti3SiC2 has been reported by manyreporters. It is generally accepted that the origin of thedecomposition is due to the out-diffusion of Si atoms andTiCx was produced as the final product. However, the initialtemperatures of the decomposition are quite conflicting andvary with different reports from 1200 ◦C [7] to 1700 ◦C [9].Most agreed that the dissociation process can be described bythe following reaction [21]:
Ti3SiC2(s) → 3TiC0.67(s) + Si(g).
It is believed that the decomposition mechanism of Ti3SiC2
has some relations with its crystalline structure, which showsa planar stacking sequence along the c-axis, consisting oftwo edge-shared layers of Ti6C octahedra that are separatedby close-packed Si atomic plane [1–3]. Two types of Ti–Cbonds are exhibited in a Ti3SiC2 unit cell. The Ti(1)–C bondadjacent to the Si layers and the Ti(2)–C bond in the centreof the unit cell. The calculated bond distance of Ti(1)–C islonger than that of Ti(2)–C, and the bond distance of Ti–Si islonger than those of both Ti(1)–C and Ti(2)–C. As a result,the Ti–C bonds are stronger than Ti–Si bond and Si is theweakest bonded element in the Ti3SiC2 structure [2, 22], whichbrings about the Si volatilization at high temperature. Inour experiment, the results are in good agreement with theexperiments under high-temperature heat treatment, that TiCx
is the major product of the reaction, while Si volatilizedinto the chamber. Elementary carbon was also detectedfrom the deposits in this experiment, indicating that the Ti–Cbonding is broken down due to the high power intensity of thevacuum arc.
5. Conclusion
We investigated the effects of vacuum arc on the erosionbehaviour of high-purity Ti3SiC2 in this article. It is seemsthat Ti3SiC2 is unstable under the impact of the vacuum arc.The dissociation of Ti3SiC2 takes place at cathode surfaceand results in the formation of TiCx . Si will be evaporatedto the vacuum chamber due to the high temperature of theelectrodes. The out-diffusion of Si has some something todo with the crystalline structure of Ti3SiC2. According tomicro-Raman results, small amounts of carbon appear onthe surface of anode as a by-product of the dissociationof Ti3SiC2, indicating that the Ti–C bonding is brokendown due to the high power intensity of the vacuum arc.Although the current used in this study is low comparedwith typical currents of real vacuum interrupters, experimentalresults obtained here can give us some knowledge about thedecomposition process of Ti3SiC2 under electrical discharge,which is vital for us to clarify the erosion mechanism ofTi3SiC2. The crater depth and the crater size are smallcompared with those metallic cathodes and the high hardnessof Ti3SiC2 can minimize the erosion caused by bridgingand mechanical deformation. Thus, as a good electricalconductor itself, if we use Ti3SiC2 as reinforcing particlesin Cu-matrix composite, it has advantages over ordinarymetallic cathode.
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Acknowledgment
This work was supported by the National Science Foundationof China (Grant no 51074077).
References
[1] Jeitschko W, Nowotny H and Benesovsky F 1967 Monatash.Chem. 98 329
[2] Zhou Y C, Sun Z M, Wang X H and Chen S Q 2001 J. Phys.:Condens. Matter 13 10001
[3] Kisi E H, Crossley J A A, Myhra S and Barsoum M W 1998J. Phys. Chem. Solids 59 1437
[4] Barsoum M W and El-Raghy T 1996 J. Am. Ceram. Soc.79 1953
[5] El-Raghy T and Barsoum M W 1999 J. Am. Ceram. Soc.82 2849
[6] Sun Z M, Hashimoto H, Zhang Z F, Yang S L and Tada S 2006Mater. Trans. 47 170
[7] Low I M, Oo Z and Prince K E 2007 J. Am. Ceram. Soc.90 2610
[8] Li S B, Xie J X, Zhao J Q and Zhang L T 2002 Mater. Lett.57 119
[9] Gao N F, Miyamoto Y and Zhang D 2002 Mater. Lett. 55 61[10] Cao W C, Liang S H, Zhang X and Yang X H 2011 Int. J.
Refract. Met. Hard Mater. 29 237
[11] Wang J B, Zhang Y, Yang M G, Ding B J and Yang Z M 2006Mater. Sci. Eng. B 131 230
[12] Wang X H, Liang S H, Yang P and Fan Z K 2009 Vacuum83 1475
[13] Takikawa H, Kusano O and Sakakibara T 1999 J. Phys. D:Appl. Phys. 32 2433
[14] Daalder J E 1976 J. Phys. D: Appl. Phys.9 2379
[15] Anders A 2009 Cathode Arcs: from fractal spotsto energetic condensation (Springer Series on Atomic,Optical, and Plasma Physics vol 50) ed G W F Drake(New York: Springer) pp 75–174
[16] Hantzsche E. 2003 IEEE Trans. Plasma Sci.31 799
[17] Mercier F, Chaix-Pluchery O, Ouisse T and Chaussende D2011 Appl. Phys. Lett. 98 081912
[18] Amer M, Barsoum M W, El-Raghy T, Weiss I, Leclair S andLiptak D 1998 J. Appl. Phys. 84 5817
[19] Qi Q, Zhang W Z, Shi L Q, Zhang W Y, Zhang W andZhang B 2012 Thin Solid Films 520 6882
[20] Boxman R L, Sanders D M and Martin P J 1995 Handbook ofVacuum Arc Science and Technology (Park Ridge, NJ:Noyes) pp 73
[21] Racault C Langlais F and Naslain R 1994 J. Mater. Sci.29 3384
[22] Bai Y L, He X D, Sun Y, Zhu C C, Li M W and Shi L P 2010Solid State Sci. 12 1220
