Mechanical properties of Ti-based glassy and nanocomposite alloys. J. Sort Departament de Física Universitat Autònoma de Barcelona

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1 Mechanical properties of Ti-based glassy and nanocomposite alloys J. Sort Departament de Física Universitat Autònoma de Barcelona 1

2 Collaborators Universitat Autònoma de Barcelona, Spain A. Hynowska, J. Fornell, E. Pellicer, A. Concustell, S. González, E. Rossinyol, S. Suriñach, M. D. Baró OCAS N.V., Zelzate, Belgium N. Van Steenberge IFW, Leibniz Institute for Solid State and Materials Research Dresden, Germany A. Gebert, J. Das, J. Eckert 2

Introduction: General Overview: Composites vs.

A) Strain hardening in nanocomposite Ti 60 Cu 14 Ni 12

B) Mechanical behavior of Ti 40 Zr 25 Ni 8 Cu 9 Be 18

3 Introduction: General Overview: Composites vs. Metallic Glasses Results and discussion: Case studies: A) Strain hardening in nanocomposite Ti 60 Cu 14 Ni 12 Sn 4 Nb 10 alloy. B) Mechanical behavior of Ti 40 Zr 25 Ni 8 Cu 9 Be 18 metallic glass. C) Mechanical behavior of Ti 60 Zr 10 Cu 38 Pd 12 metallic glass. Conclusions Outline 3

4 Introduction Requirement of biomaterials (for orthopedic applications) High strength and low Young s modulus (in bone: 4 to 30 GPa) avoid loosening of the implant. Biocompatibility: host response and the materials degradation - not toxic elements: Ni, Co, Al, Be, V, High corrosion and wear resistance. Good Osseointegration (surface chemistry, surface roughness and topography) Up to now Conventional biomaterials Stainless steel (Co-Cr) alloys Ti-6Al-4V Limitations - Ni, Co, Cr toxic effect (dermatitis, carcinogeicity ) - Too high Young s modulus - Release of Al and V (long term health problems), V is toxic. - Not high shear strength. - Limited implants life (10-15 years). 4

5 Introduction Why is titanium so much used in biomedical field? Besides good anticorrosion behavior and biocompatibility: Strong, yet light weight: Ti is 56% as dense as steel with yield stress twice that of stainless steel. High strength-to-weight ratio. Density similar to bone. Flexible: Ti elastic modulus and coefficient of thermal expansion not far from human bone. Easily workable: Ti can be machined using conventional metal processing tools. Others: non-magnetic (allows NMR, no interactions with magnetic fields, 7 th most abundant element in Earth). 5

6 Introduction The Young s modulus of different implant materials Young s modulus (GPa) 6

Body centered cubic (bcc), or -Ti, typically found above 1156 K.

7 Introduction Ti-based crystalline materials Hexagonal close-packed (hcp), or -Ti, typically found at room temperature. Body centered cubic (bcc), or -Ti, typically found above 1156 K. Titanium can retain the -phase at room temperature after allotropic transformations. 7

8 -Ti vs. -Ti phase alloys Alloying elements stabilizers Al, O, N Introduction type Ti alloys are getting attention because of their lower Young s modulus (E GPa) as compared to type Ti alloys (E GPa). stabilizers Mo, V, Nb, Ta, W, Fe, Mn, Cu, Ni, Cr Neutral Zr, Si, Sn and near- alloys: Ti-2.5Cu, Ti-5Al-2.5Sn, Ti-8Al-1V- 1Mo, Ti-5Al-5Sn-2Zr-2Mo, + alloys: Ti-6Al-4V, Ti-6Al-6V-4Sn, Ti-8Al-1Mo-1V, Ti-6Al-2Sn-2Zr-2Cr-2Mo, alloys: Ti-13V-11Cr-3Al, Ti-10V-2Fe-3Al,TiFe-3.85Sn 8

9 Introduction Not only the composition but also the microstructure is important! The fatigue limit of ultra-fine grained commercial purity titanium depends strongly on its microstructure. Strengthening of commercial titanium occurs after equal channel angular pressing (ECAP) in combination with other deformation processes. H. J. Rack, J.I. Qazi, Mater. Sci. Engi. C 26 (2006)

$fracture toughness Promising tribological and wear properties High fatigue limits and corrosion$

10 Why metallic glasses? Introduction Metallic glasses (MGs) are amorphous metallic alloys i.e. do not exhibit long-range order. Unique properties Lower Young s modulus (elastic softening) Large elastic elongation Higher strength and fracture toughness Promising tribological and wear properties High fatigue limits and corrosion resistance Applications: Biomedical Electronic devices Sporting goods Aerospace technologies. 10

11 Metallic glasses vs. other materials Introduction Metallic glasses exhibit high yield strength compared to other materials, but limited plasticity at room temperature. Ti-based metallic glasses exhibit rather large Young s modulus. Mg-based metallic glasses show lower Young s modulus but they are biodegradable and dissolve at high rates in simulated body fluids. 11

biomaterials for orthopedic implants - First Ti-based BMGs contained toxic

12 Introduction Ti-based metallic glasses High strength High elastic limit Low Young s modulus Excellent corrosion resistance Good bioactivity of Ti element Suitable biomaterials for orthopedic implants - First Ti-based BMGs contained toxic elements (i.e., Ti-Zr-Ni-Be system) [A. Peker, W.L. Johnson, US Patent 5, 288, 344 (1994)]. 12

13 Introduction First Ti-based metallic glasses: Ti-Zr-Ni-Cu-Be These materials can be fabricated in large sizes and show reasonable compressive plasticity BUT Beryllium is highly toxic! Mei Jinna, PhD Thesis (2009) 13

Introduction First Ti-based metallic glasses: Ti-Ni-Cu base Mei Jinna, PhD Thesis (2009) These alloys exhibit similar yield stress as the Ti-Zr-Ni-Cu-Be system, but plastic strain is much lower (i.e., they are very brittle).

14 Introduction First Ti-based metallic glasses: Ti-Ni-Cu base Mei Jinna, PhD Thesis (2009) These alloys exhibit similar yield stress as the Ti-Zr-Ni-Cu-Be system, but plastic strain is much lower (i.e., they are very brittle). Moreover, Ni and Cu are not so good in terms of biocompatibility. New non-toxic Ti-based BMGs developed in recent years: Ti-Zr-Cu-Pd-Sn [F.X. Qin et al., Mater Trans. 48 (2006) 515] Ti-Zr-Cu-Pd [F.X. Qin et al.,intermetallics. 15 (2007) 1337; S.L. Zhu et al., Mater. Sci. Eng. A 459 (2007) 233]. 14

How do metallic glasses deform? Introduction Plastic flow in metallic glasses (MGs) is accompanied by dilatation (i.e., creation of excess free volume). Single atomic jumps Spaepen, Acta Metall.

15 How do metallic glasses deform? Introduction Plastic flow in metallic glasses (MGs) is accompanied by dilatation (i.e., creation of excess free volume). Single atomic jumps Spaepen, Acta Metall. 1977;25:407. Plastic flow equation: 0v0 0v0 2 fcf k f sinh 2k T B γ : Shear transformation zones Argon, Acta Metall. 1979;27:47 Falk and Langer. Phys. Rev. E 1998;57:7192. is the shear strain rate c f = exp (- v * /<v f >) flow defect concentration k B Boltzmann constant k f temperature-dependent rate constant f volume fraction of potential flow units is the shear stress 0 0: activation volume for a flow event and : atomic volume. 15

16 How do metallic glasses deform? Introduction At room temperature, the excess free volume tends to coalesce into shear bands, leading to local viscosity drops Shear bands inside and around an indent performed on a Ti-based MG Consequences in the nanoindentation experiments: Serrations (pop-in events) in the loading curves Inhomogeneous plastic flow occurs for T< 0.8T g. Premature fracture occurs, unless prevented by partial nanocrystallization. 16

17 Introduction Strategies to enhance mechanical properties To refine the microstructure of -Ti alloys towards the nanometer scale (to increase hardness keeping a low Young s modulus). To find new families of metallic glasses, free from toxic/allergic elements, with good glass forming ability (to manufacture samples with reasonable sizes) and high hardness combined with low Young s modulus. To perform suitable heat treatments of existing metallic glasses to tailor the microstructure and avoid their premature failure (partial nanocrystallization to form nanocomposites). 17

18 CASE STUDY # 1: Hardening mechanisms in a Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 nanocomposite alloy A. Concustell et al., J. Mater. Res. 24 (2009)

19 Results & Discussion Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Nano-composite alloy: Micrometer size β-ti dendrites. Nanoestructured eutectic matrix. Good mechanical properties: high strength, large plasticity AIMS of the WORK: Study of the mechanical behaviour by nanoindentation and compression tests: evidence for strain hardening. The contribution of the different constituent phases to the overall strain hardening. Find out the microstructural mechanisms responsible for this strain hardening. 19

20 Results & Discussion Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Processing: Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 = 3 mm rods As-cast sample Arc melting + Copper mold casting Deformed samples Compressed to different strain levels Characterization X-ray Diffraction (XRD) Phase identification Scanning Electron Microscopy (SEM) Analysis of the microstructure of the as-cast and deformed specimens. Transmission Electron Microscopy (TEM) Microstructural characterization and deformation mechanisms Nanoindentation: A diamond pyramidal-shaped (Berkovich-type) indenter Load control mode; Forces of 1.5 and 500 mn Hardness calculated by Oliver-Pharr method 20

21 Results & Discussion XRD SEM Dendrites Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Intermetallic Eutectic Ti Cu Ni Sn Nb Dendrites E. matrix E. rod

$8*10-4 s -1 2000 1500 1000 500 0 0 2 4 6 8 10 12 14 Strain (%) fracture E = 75 MPa Yield strength (as cast) = 1400 MPa Fracture strength = 2200 MPa$

22 Stress (MPa) Results & Discussion Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Compression tests Nanoindentation Continuous work hardening 2500 Strain rate: 1.8*10-4 s Strain (%) fracture E = 75 MPa Yield strength (as cast) = 1400 MPa Fracture strength = 2200 MPa 22 22

23 Results & Discussion Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 intermetallic eutectic dendrite 23 23

24 F (mn) F (mn) Results & Discussion Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 1,6 1,4 1,2 1,0 dendrites eutectic As cast 1,6 1,4 1,2 1,0 dendrites eutectic 12% deformed 0,8 0,8 0,6 0,6 0,4 0,4 0, h (nm) 0, h (nm) F max : 1.5 mn 24 24

25 H (GPa) Results & Discussion Nanoindentation results Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 8,5 8,0 F max = 1.5 mn In the as-cast state, dendrites are harder (solution hardening) than eutectic matrix. 7,5 7,0 6,5 Eutectic matrix strengthens more than the dendrites as deformation proceeds. 6,0 5,5 H den H eut H CuTi (%) The hard CuTi 2 intermetallic phase remains unaltered. 25

26 Results & Discussion X-ray diffraction results Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Broadening of the XRD peaks: - Grain size refinement in the different phases (grain boundary hardening) - Increase of microstrains 26

27 Results & Discussion TEM results Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Eutectic matrix HRTEM Dislocation-induced strain hardening!? 2 0 n m -Ti rod Eutectic dislocations p = 9% Inverse FFT nm 27

Results & Discussion XRD & TEM results Evidence for a

B2 phase Austenite Monoclinic B19 phase Martensite NiTi B2

located at the eutectic matrix Dark field This phase

28 Results & Discussion XRD & TEM results Evidence for a martensitic transformation Ti 60 Cu 14 Ni 12 Sn 6 Nb 10 Cubic B2 phase Austenite Monoclinic B19 phase Martensite NiTi B2 phase is almost supressed at 12% deformation The B19 phase is located at the eutectic matrix Dark field This phase transformation probably contributes to the local hardening of the eutectic matrix. 28

29 CASE STUDY # 2: Mechanical behaviour of Ti 40 Zr 25 Ni 8 Cu 9 Be 18 metallic glass: a nanoindentation study J. Fornell et al., Int. J. Plast. 25 (2009)

30 Results & Discussion Ti 40 Zr 25 Ni 8 Cu 9 Be 18 Metallic glass rods ( = 3 mm) prepared by Cu-mold casting Characterization Structural and thermal properties investigated by X-ray diffraction and differential scanning calorimetry. Nanoindentation tests: Nanoindenter XP (MTS) and UMIS (Fischer-Cripps Lab.) Diamond pyramidal-shaped (Berkovich-type) tip. Load control mode: - Range of forces: mn. - Range of loading rates: mn/s Displacement control mode: - Range of loading rates: nm/s Hardness evaluated using the method of Oliver and Pharr at the end of load holding segments. 30

Results & Discussion Nanoindentation results Ti 40 Zr 25 Ni 8 Cu 9 Be 18 Pop-in events observed during loading P Max = 100 mn Inhomogeneous plastic flow expected since: 1 dh

31 Results & Discussion Nanoindentation results Ti 40 Zr 25 Ni 8 Cu 9 Be 18 Pop-in events observed during loading P Max = 100 mn Inhomogeneous plastic flow expected since: 1 dh h dt RT T g 0.49 Deformation map from: Schuh et al., Acta Mater. 2007, 55, 4067 H (GPa) E (GPa) Nanoindentation Compression Nanoindentation 6.9 (10 mn) 6.3 (100 mn)

$sin 2 C C 0.194 M-C is the internal friction coefficient) C is the fracture angle (39.5º 45º) Mohr-Coulomb, not Tresca!$ Simulations confirm pressure-sensitive yielding: The elastic (Herzian) solution is far from the experimental data.

Simulations confirm pressure-sensitive yielding: The elastic (Herzian) solution is far from the experimental data.

32 Results & Discussion Compression and Finite-element simulations Ti 40 Zr 25 Ni 8 Cu 9 Be 18 Application of the Mohr-Coulomb yield criterion: y 0 M C n M C cos2 sin 2 C C M-C is the internal friction coefficient) C is the fracture angle (39.5º 45º) Mohr-Coulomb, not Tresca! Simulations confirm pressure-sensitive yielding: The elastic (Herzian) solution is far from the experimental data. The Tresca criterion overestimates the maximum penetration depth. Finite element simulations, Strand7 software, developed by G+D Computing Pty Ltd. The Mohr-Coulomb criterion allows for proper adjustment of the experimental nanoindentation data. 32

33 Results & Discussion Finite-element simulations Ti 40 Zr 25 Ni 8 Cu 9 Be 18 Displacement and circumferential stress ( θθ ) contour mappings Application of the Mohr-Coulomb yield criterion results in an extended plastic zone beneath the indenter In agreement with: Narashiman Mech. Mater. 2004,36, 633 Similar conclusions about yielding of metallic glasses (obtained from simulations) by: Vaidyanathan et al., Acta Mater. 2001, 49, 3781 Anand and Su, J. Mech. Phys. Solids, 2005, 53, 1362 Schuh et al., Acta Mater. 2007, 55,

34 CASE STUDY # 3: Mechanical behaviour of Ti 60 Zr 10 Cu 38 Pd 12 glassy and nanocomposite materials J. Fornell et al., J. Mech. Behav. Biomed. Mater. 4 (2011)

35 Sample: Ti 40 Zr 10 Cu 38 Pd 12 metallic glass prepared by arc-melting and subsequent copper mould casting (rods = 2 mm) Heat treatments: Annealing was performed for 30 min, in vacuum, at: T ann,1 = 713 K (T g < T ann,1 < T x1 ) T ann,2 = 738 K (T x1 < T ann,2 < T x2 ) T ann,3 = 923 K (T ann,3 > T x2 ) Addition of Nb: Results & Discussion Ti 40 Zr 10 Cu 38 Pd 12 Fabrication of = 2 mm rods with composition (Ti 40 Zr 10 Cu 38 Pd 12 ) 1-x Nb x ( x = 0, 2, 3, 4) by suction casting. 35

36 Results & Discussion Ti 40 Zr 10 Cu 38 Pd 12 Structure and thermal stability: Structural and thermal properties investigated by X-ray diffraction and differential scanning calorimetry. Mechanical characterization: Uniaxial compression tests of the Ti-based bulk metallic glass and devitrified material (strain rate s -1 ). Nanoindentation tests: UMIS (Fischer-Cripps Lab.) Diamond pyramidal-shaped (Berkovich-type) tip. Load control mode Maximum load: 250 mn Finite element simulations of nanoindentation curves using the Strand7 software, developed by G+D Computing Pty Ltd. 36

Results & Discussion XRD and DSC results Ti 40 Zr 10 Cu 38 Pd 12 Amorphous nature and thermal stability of the Ti 60 Zr 10 Cu 38 Pd 12 sample XRD and TEM (SAED

37 Results & Discussion XRD and DSC results Ti 40 Zr 10 Cu 38 Pd 12 Amorphous nature and thermal stability of the Ti 60 Zr 10 Cu 38 Pd 12 sample XRD and TEM (SAED pattern) reveal that the as-cast sample is fully amorphous Glass transition temperature: T g = 685 K Crystallization temperatures: T x1 = 720 K T x2 = 795 K 37

$Results & Discussion Ti 40 Zr 10 Cu 38 Pd 12 Compression test As-cast alloy Upon compression, reasonable plasticity, fracture at ~ 2.7% total strain. Tough behaviour expected since J.$

38 Results & Discussion Ti 40 Zr 10 Cu 38 Pd 12 Compression test As-cast alloy Upon compression, reasonable plasticity, fracture at ~ 2.7% total strain. Tough behaviour expected since J.J. Lewandowski et al., Phil. Mag. Lett. 85 (2005) 77 Serrated flow behaviour Shear band activity. M C cos2 sin 2 F F F 42 º 45 º Evidence for the Mohr-Coulomb yield criterion Dimple size in the fracture surface around m. Fracture angle 42º. The Mohr- Coulomb coefficient is therefore 0.105, in agreement with other Tibased MGs (J. Sort et al., Int. J. Plast. 25 (2009) 1540). 38

The Mohr-Coulomb criterion allows for proper adjustment of the experimental nanoindentation data

39 Results & Discussion Finite-element Simulations Ti 40 Zr 10 Cu 38 Pd 12 The Tresca yield criterion (typical of polycrystalline alloys) overestimates the penetration depth. The Mohr-Coulomb criterion allows for proper adjustment of the experimental nanoindentation data using: M-C = (cohesion) = 0.9 GPa E (Young s modulus) = 100 GPa y 0 M C n Indentation response of as-cast alloy 39

40 Results & Discussion XRD and TEM results after heat-treatments Ti 40 Zr 10 Cu 38 Pd 12 As-cast T ANN1 = 738 K T ANN2 = 923 K T ANN2 = 923 K The glassy structure of the as-cast alloy developes into a nanocomposite material at T ANN1 and a fully crystalline alloy at T ANN2 40

41 Results & Discussion Elastic properties vs. Annealing temperature Ti 40 Zr 10 Cu 38 Pd 12 Relatively high Poisson s ratio (some plasticity expected) Relatively low Young s modulus (E Ti-6Al4V = 110 GPa) E and G increase after crystallization, in agreement with other metallic glasses ( elastic softening, due to free volume and the highly cooperative shear under the action of small stress). (T.C. Hufnagel et al. PRB 73 (2006) ) E: Young s modulus G: Shear modulus K: Bulk modulus : Poisson s ratio 41

42 Results & Discussion Mechanical properties vs. Annealing temperature Ti 40 Zr 10 Cu 38 Pd 12 The hardness of Ti 60 Zr 10 Cu 38 Pd 12 is larger than for Ti-6Al-4V. The reduced Young s modulus of Ti 60 Zr 10 Cu 38 Pd 12 is lower than for Ti-6Al- 4V. Both H and E r tend to increase with T ANN, due to several microstructural effects: Reduction of free volume during structural relaxation. Crystallization of high-strength phases, such as: CuTi 2, CuZr 2 (intermetallic phases). The wear resistance of Ti 60 Zr 10 Cu 38 Pd 12 (H/E r ~ ) is higher than for Ti-6Al-4V (H/E r = 0.04). 42

43 Results & Discussion Influence of Nb addition (Ti 40 Zr 10 Cu 38 Pd 12 ) 1-x Nb x X = 0 X = 3 X = 4 Metallic glass Nanocomposite Polycrystalline Nanocrystallization induces a drastic increase of plasticity 43

44 In conclusion A few issues to be considered (from a mechanical viewpoint): Search for processing routes to induce strengthening (e.g., grain size refinement) of nanocomposite materials without compromising the Young s modulus. Search for metallic glasses with non-toxic elements, reasonable sample sizes, low Young s modulus, large hardness and enhanced plasticity. Search for nanocomposite materials (nanocrystals embedded inside metallic glass matrices) with enhanced plasticity: In-situ growth of the composite materials (particles dispersed during casting) Thermally-induced nanocrystallization Mechanically-driven nanocrystallization Acknowledgements Financial support from the 2009SGR-1292, MAT and BioTiNet research projects 44

Mechanical properties of Ti-based glassy and nanocomposite alloys. J. Sort Departament de Física Universitat Autònoma de Barcelona

Mechanical properties of Ti-based glassy and nanocomposite alloys J. Sort Departament de Física Universitat Autònoma de Barcelona 1 Collaborators Universitat Autònoma de Barcelona, Spain A. Hynowska, J.