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Fatigue behavior of highly porous titanium produced by powder metallurgy
M. Bram1, S. Özbilen2, D. Liebert1, T. Beck3, O. Guillon1
1Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, 52425 Jülich, Germany2Gazi University, Faculty of Technology, Department of Metallurgical and Materials Engineering, Teknikokullar, Ankara, Turkey.3Lehrstuhl für Werkstoffkunde (WKK), Technische Universität Kaiserslautern, D‐67663 Kaiserslautern, Germany.
DGM WerkstoffwocheDresden, 14. ‐ 18.09.2015
2 Martin Bram, Dresden, 16.09.2015
Outline
Applications of porous titanium Powder metallurgical processing of porous titanium Influence of interstitial contents on mechanical properties Fatigue testing with varying interstitial contents Results Conclusions
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Well known are biomedical applications of porous titanium…
Synthes Biomet Biomet Centerpulse
Spine implant Cone augmentsAcetabular shell Knee implant
Less known are …
Porous titanium(current collector)
Application in electrochemical devices and filters: Current collector for PEM‐electrolysis cells Porous substrates in lead‐acid batteries Filter/catalyst support under harsh conditions
PEM electrolysis cell
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Powder metallurgical production of porous titanium
P/M with temporary space holder: Pressing Ti powder/space holder mixtureMachining in the unsintered state Decomposition of space holder Sintering
Synthes
Spine implant
Other similarP/M technologies
are in use
Additive manufacturing: CAD model Virtual slices of CAD data Selective melting of a powder bed by electron beam or laser
Secondary operations
Patient‐specific implants
Source: arcam
Wet chemical processing: Tape casting/Screen printing Debinding Sintering
Surface ofcurrent collectorPEM electro‐lysis cell
40 µm
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Sources for interstitial elements
Graphite‐crucible during gas atomizationof the powder carbon
Gasatomization with argon residual oxygen, nitrogen
Residuals from organic binders carbon, oxygen
Sintering atmosphere (vacuum, argon) residual oxygen, nitrogen
Titanium‐lattice: high solubility of O,C,N Increased strength, reducedductility due to interstitials:
hexagonal‐Ti lattice
O,C,N atomssolved asinterstitialelements
NCOeq cccO 275.0Oxygen‐equivalent (Conrad1966)
H. Conrad, Acta Met., 14 (1966) 1631 – 1633.
Uptake of interstitial elements (O,C,N)during processing of Ti powders
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Influence of interstitial contents on characteristic properties of titanium and titanium alloys
Ti Grade1Ti Grade2Ti Grade3Ti Grade4Ti‐6Al‐4V Gr.5Ti‐6Al‐4V Gr.23Ti‐6Al‐7Nb
Omax.[wt%]0.180.250.350.400.200.130.20
d0.2[MPa]170275380483828759800
max.[MPa]240345450550895828900
f (min)[%]24201815101010
Norm
ASTM B 348ASTM B 348 ASTM B 348 ASTM B 348ASTM B 348ASTM B 348ASTM F 1295
Cmax.[wt%]0.100.100.100.100.100.100.10
How can these relationships be transfered to porous titanium and its fatigue behavior ?
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Manufacturing of porous titaniumwith well defined interstitial contents
Ti powder, gas atomized (GA)(TLS, Bitterfeld, Germany)
d50 = 33 µm0.166 wt.% O0.004 wt.% C
Ti powder, hydr./dehydr. (HDH) (GFE, Nuremberg, Germany)
d50 = 48.3 µm0.355 wt.% O0.016 wt.% C
Series C: GA powderWarm compaction with binder
Porosity: 62.0 %0.580 wt.% O0.076 wt.% C
Series A: GA + HDH powdersCold compaction65.0 % porosity0.336 wt.% O0.006 wt.% C
Series B: HDH powdersCold compaction63.9 % porosity0.443 wt.% O0.012 wt.% C
Ratio Ti/space holder = 30/70Cold/warm compaction
Sintering 1300°C, 3h, vacuum 8mmh 11 mm
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Strategy of fatigue testing
tmax
min
Tension
Compression
Cyclic compression/compression tests: Ambient temperature Sinusoidal loading Frequency 6 Hz Stress level: min = 0.15∙d0.2 (from static compression test) Abort criterion: 5% (20%) plastic deformation
or 4 million load cycles R = 10, 5, 2 2 samples for each parameter set
Static compression tests to define min: Ambient temperature Strain rate 10‐3 s‐1 Abort criterion: 30% plastic deformation 2 samples for each parameter set
Series A (0.336 wt.% O) min = ‐ 35.0 MPaSeries B (0.443 wt.% O) min = ‐ 46.0 MPaSeries C (0.580 wt.% O) min = ‐ 57.0 MPa
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Three stages of fatigue
Strain at max
Strain at min
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Fatigue results of series A ‐ C
Series A: 0.336 wt.% O Series B: 0.443 wt.% O Series C: 0.580 wt.% O
1.37∙105 cycles7.86∙104 cycles
5.34∙104 cycles6.03∙104 cycles
5.57∙104 cycles5.62∙104 cycles
cycles tofailure
Metallographical preparationto analyse the failure behavior:
Series A: Sample with 5% deformationSeries B: Sample with 5% deformationSeries C: Sample with 20% deformation
20%
5%
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Microstructure of samples from series A,B(Fatigue test stopped at 5% deformation)
Series A: 0.336 wt.% O Series B: 0.443 wt.% O
no obvious cracks were foundafter 1.6∙105 cycles ductile deformation
crack formation at positions 1,2,3after 8.0∙104 cycles
30°A B
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Microstructure, sample series B, position 2Cross section, overview
SEM detail, position 2
B
B
S = crack initiationat the surface
P =crack initiationat micropores
IF = intergranularfacture
TF =transgranularfacture
B
B
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Microstructure, sample series B, position 2
B B
Electron backscatter diffraction (EBSD) EBSD ‐ Local misorientation
Areas of high plastic deformation
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Microstructure of sample from series C(Fatigue test stopped at 20% deformation)
30°
Brittle behaviour, formation of crush band
30°
C
after 1.1∙105 cycles
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Series A: Variation of R and min
tmax
min
Tension
Compression
min = ‐ 35.0 MPa, R = 10
1.37∙105 cycles7.86∙104 cycles
cycles tofailure
Approach 1: Decrease of R to 5 and 2
Approach 2: Decrease of min
min = ‐ 35.0 MPa, R = 2min = ‐ 35.0 MPa, R = 5
8.55∙105 cycles1.97∙106 cycles
> 4∙106 (abort criterion)
0.9∙min R = 10 0.8∙min R = 10
> 4∙106 > 4∙106
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Summary and conclusion
P/M processing of porous titanium with variation of interstitial content
Series A: 0.336 wt.% O; No crack formation found (after 105 cycles, 5% deformation) Decrease of R and min 4∙106 cycles w/o failure
Fatigue testing in compression/compression modemin = 0.15∙d0.2; variation of R = 10, 5, 2; variation of min
Series B: 0.443 wt.% O; Formation of first cracks (after 5∙104 cycles, 5% deformation)
Series C: 0.580 wt.% O; Brittle fracture, formation of crush bands (after 5∙104 cycles, 5%, 20% deformation)
17 Martin Bram, Dresden, 16.09.2015
Thank you for your attention !
Thanks to all colleagues at IEK‐1