44
Mechanical properties of Ti-based glassy and nanocomposite alloys J. Sort Departament de Física Universitat Autònoma de Barcelona 1
Mechanical properties of Ti-based
glassy and nanocomposite alloys
J. Sort Departament de Física
Universitat Autònoma de Barcelona
1
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
Collaborators
2
• Introduction:
General Overview: Composites vs. Metallic Glasses
• Results and discussion:
Case studies:
A) Strain hardening in nanocomposite Ti60Cu14Ni12Sn4Nb10 alloy.
B) Mechanical behavior of Ti40Zr25Ni8Cu9Be18 metallic glass.
C) Mechanical behavior of Ti60Zr10Cu38Pd12 metallic glass.
• Conclusions
Outline
3
4
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)
Conventional
biomaterials Limitations
Stainless steel
(Co-Cr) alloys
- Ni, Co, Cr toxic effect
(dermatitis, carcinogeicity…)
- Too high Young’s modulus
Ti-6Al-4V
- Release of Al and V
(long term health problems),
V is toxic.
- Not high shear strength.
- Limited implants life (10-15 years).
Up to now…
Introduction
5
Why is titanium so much used in biomedical field?
Introduction
• 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, 7th
most abundant element in Earth).
6
Introduction
Young’s modulus (GPa)
The Young’s modulus of different implant materials
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.
8
Introduction -Ti vs. -Ti phase alloys
• 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 …
type Ti alloys are getting attention because
of their lower Young’s modulus (E ≈ 55-100
GPa) as compared to type Ti alloys (E ≈
100-150 GPa).
Alloying elements
• stabilizers
Al, O, N
• stabilizers
Mo, V, Nb, Ta, W, Fe,
Mn, Cu, Ni, Cr
•Neutral
Zr, Si, Sn
9
H. J. Rack, J.I. Qazi, Mater. Sci. Engi. C 26 (2006) 1269-1277
• 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.
Not only the composition but also the microstructure is important!
Introduction
10
• 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.
Why metallic glasses? Introduction
11
Introduction
Metallic glasses vs. other materials
• 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.
12
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)].
Introduction
13
Introduction
• First Ti-based metallic glasses: Ti-Zr-Ni-Cu-Be
Mei Jinna, PhD Thesis (2009)
These materials can
be fabricated in large
sizes and show
reasonable
compressive
plasticity
BUT
Beryllium is highly
toxic!
14
• First Ti-based metallic glasses: Ti-Ni-Cu base
Introduction
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].
Introduction
How do metallic glasses deform?
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. Shear transformation zones Argon, Acta Metall. 1979;27:47
Falk and Langer . Phys. Rev. E 1998;57:7192.
Tk
vvkfc
B
ff2
sinh2 0000 kB Boltzmann constant
kf temperature-dependent rate constant
f volume fraction of potential flow units
is the shear stress is the shear strain rate
0 0: activation volume for a flow event and : atomic volume.
:γ
cf = exp (- v*/<vf>) flow defect concentration
Plastic flow equation:
15
16
At room temperature, the excess free volume tends to coalesce into
shear bands, leading to local viscosity drops
Consequences in the nanoindentation experiments:
Serrations (pop-in events) in the loading curves
Inhomogeneous plastic flow occurs for T< 0.8Tg. Premature fracture
occurs, unless prevented by partial nanocrystallization.
Shear bands inside and around an
indent performed on a Ti-based MG
Introduction
• How do metallic glasses deform?
17
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).
Introduction
18
CASE STUDY # 1:
“Hardening mechanisms in a
Ti60Cu14Ni12Sn6Nb10 nanocomposite alloy”
A. Concustell et al., J. Mater. Res. 24 (2009) 3146-3153.
19
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.
Results & Discussion Ti60Cu14Ni12Sn6Nb10
20
Processing: Ti60Cu14Ni12Sn6Nb10 = 3 mm rods
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
• As-cast sample • Deformed samples
Compressed to different strain levels
Results & Discussion
Arc melting + Copper mold casting
Ti60Cu14Ni12Sn6Nb10
21
XRD
SEM
Intermetallic
Dendrites
Eutectic
Ti Cu Ni Sn Nb
Dendrites 58.28 10.22 2.74 5.36 23.38
E. matrix 64.35 11.72 10.49 1.86 11.57
E. rod 72.15 10.47 3.07 1.45 12.84
Results & Discussion Ti60Cu14Ni12Sn6Nb10
22
22
Continuous work hardening
Compression tests Nanoindentation
fracture
E = 75 MPa
Yield strength (as cast) = 1400 MPa
Fracture strength = 2200 MPa
Strain rate: 1.8*10-4 s-1
0 2 4 6 8 10 12 140
500
1000
1500
2000
2500
Str
ess (
MP
a)
Strain (%)
Results & Discussion Ti60Cu14Ni12Sn6Nb10
23
23
dendrite eutectic intermetallic
Results & Discussion Ti60Cu14Ni12Sn6Nb10
24
24 Fmax: 1.5 mN
40 60 80 100
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
F (
mN
)
h (nm)
dendrites
eutectic
As cast
40 60 80 100
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
dendrites
eutectic
F (
mN
)h (nm)
12% deformed
Results & Discussion Ti60Cu14Ni12Sn6Nb10
25
In the as-cast state, dendrites
are harder (solution hardening)
than eutectic matrix.
Eutectic matrix strengthens
more than the dendrites as
deformation proceeds.
The hard CuTi2 intermetallic
phase remains unaltered.
0 2 4 6 8 10 12 145,5
6,0
6,5
7,0
7,5
8,0
8,5
Fmax
= 1.5 mN
H den
H eut
H CuTi2
H (
GP
a)
(%)
Results & Discussion
Nanoindentation results Ti60Cu14Ni12Sn6Nb10
26
• Broadening of the XRD peaks: - Grain size refinement in the different phases (grain boundary hardening) - Increase of microstrains
Results & Discussion
X-ray diffraction results Ti60Cu14Ni12Sn6Nb10
27
27
2 0 n m
HRTEM
Eutectic
-Ti
rod
200 nm
dislocations
Inverse
FFT
Dislocation-induced strain
hardening !?
Eutectic
matrix
Results & Discussion TEM results Ti60Cu14Ni12Sn6Nb10
p = 9%
28
Dark field
Evidence for a martensitic transformation
Monoclinic B19’ phase
Austenite Martensite
The B19’ phase is
located at the
eutectic matrix
NiTi B2 phase is almost
supressed at 12% deformation
This phase transformation
probably contributes to the local
hardening of the eutectic matrix.
Results & Discussion
XRD & TEM results
Cubic B2 phase
Ti60Cu14Ni12Sn6Nb10
29
CASE STUDY # 2:
“Mechanical behaviour of Ti40Zr25Ni8Cu9Be18
metallic glass: a nanoindentation study”
J. Fornell et al., Int. J. Plast. 25 (2009) 1540-1559.
30
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: 4 - 500 mN.
- Range of loading rates: 0.4 – 6.4 mN/s
• Displacement control mode: - Range of loading rates: 2.6 – 20 nm/s
• Hardness evaluated using the method of Oliver and Pharr at the end of load holding segments.
Results & Discussion Ti40Zr25Ni8Cu9Be18
31
dt
dh
h
1
• Pop-in events observed during loading
• Inhomogeneous plastic flow expected since:
49.0gT
RT 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)
98 105
PMax = 100 mN
Results & Discussion
Nanoindentation results Ti40Zr25Ni8Cu9Be18
32
nCMy 0
Application of the Mohr-Coulomb yield criterion:
194.02sin
2cos
C
CCM
Simulations confirm pressure-sensitive yielding:
• The elastic (Herzian) solution is far from the
experimental data.
• The Tresca criterion overestimates the maximum
penetration depth.
• The Mohr-Coulomb criterion allows for proper
adjustment of the experimental nanoindentation data. Finite element simulations,
Strand7 software, developed by G+D Computing Pty Ltd.
C is the fracture angle (39.5º ≠ 45º)
Results & Discussion
Mohr-Coulomb, not Tresca!
M-C is the internal friction coefficient)
Compression and Finite-element simulations
Ti40Zr25Ni8Cu9Be18
33 33
• 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, 4067
Results & Discussion
Finite-element simulations Ti40Zr25Ni8Cu9Be18
34
CASE STUDY # 3:
“Mechanical behaviour of Ti60Zr10Cu38Pd12
glassy and nanocomposite materials”
J. Fornell et al., J. Mech. Behav. Biomed. Mater. 4 (2011) 1709-1717.
35
Sample:
Ti40Zr10Cu38Pd12 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:
Tann,1 = 713 K (Tg < Tann,1 < Tx1)
Tann,2 = 738 K (Tx1 < Tann,2 < Tx2)
Tann,3 = 923 K (Tann,3 > Tx2)
Results & Discussion Ti40Zr10Cu38Pd12
Addition of Nb:
Fabrication of = 2 mm rods with composition (Ti40Zr10Cu38Pd12)1-xNbx ( x = 0, 2, 3, 4)
by suction casting.
36
Mechanical characterization:
– Uniaxial compression tests of the Ti-based bulk metallic glass
and devitrified material (strain rate 1.8·10-4 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.
Results & Discussion Ti40Zr10Cu38Pd12
Structure and thermal stability:
Structural and thermal properties investigated by X-ray diffraction and
differential scanning calorimetry.
37
• XRD and TEM (SAED pattern)
reveal that the as-cast sample is
fully amorphous
• Glass transition temperature: Tg = 685 K
• Crystallization temperatures: Tx1 = 720 K
Tx2 = 795 K
Amorphous nature and thermal stability of the Ti60Zr10Cu38Pd12 sample
Results & Discussion
XRD and DSC results Ti40Zr10Cu38Pd12
38
105.02sin
2cos
F
FCM
º45º42F
Evidence for the Mohr-Coulomb yield criterion
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.
• Dimple size in the fracture
surface around 15-20 m.
• Fracture angle 42º. The Mohr-
Coulomb coefficient is therefore
0.105, in agreement with other Ti-
based MGs (J. Sort et al., Int. J.
Plast. 25 (2009) 1540).
Results & Discussion
Compression test
Ti40Zr10Cu38Pd12
39
• 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 = 0.105
0 (cohesion) = 0.9 GPa
E (Young’s modulus) = 100 GPa
nCMy 0
Indentation response of as-cast alloy
Results & Discussion
Finite-element Simulations Ti40Zr10Cu38Pd12
40
As-cast TANN1 = 738 K
TANN2 = 923 K TANN2 = 923 K
• The glassy structure of the as-cast
alloy developes into a nanocomposite
material at TANN1 and a fully crystalline
alloy at TANN2
Results & Discussion
XRD and TEM results after heat-treatments Ti40Zr10Cu38Pd12
41
• Relatively high Poisson’s ratio
(some plasticity expected)
• Relatively low Young’s modulus
(ETi-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) 064204)
E: Young’s modulus
G: Shear modulus
K: Bulk modulus
: Poisson’s ratio
Results & Discussion
Elastic properties vs. Annealing temperature Ti40Zr10Cu38Pd12
42
• The hardness of Ti60Zr10Cu38Pd12 is
larger than for Ti-6Al-4V.
• The reduced Young’s modulus of
Ti60Zr10Cu38Pd12 is lower than for Ti-6Al-
4V.
• Both H and Er tend to increase with
TANN, due to several microstructural
effects:
• Reduction of free volume during
structural relaxation.
• Crystallization of high-strength
phases, such as: CuTi2, CuZr2
(intermetallic phases).
• The wear resistance of Ti60Zr10Cu38Pd12 (H/Er ~ 0.06 - 0.07) is higher than for Ti-6Al-4V (H/Er = 0.04).
Results & Discussion
Mechanical properties vs. Annealing temperature Ti40Zr10Cu38Pd12
43
Influence of Nb addition
X = 0 X = 3 X = 4
Metallic glass Nanocomposite Polycrystalline
Results & Discussion (Ti40Zr10Cu38Pd12)1-xNbx
Nanocrystallization induces a
drastic increase of plasticity
44
• 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
In conclusion …
Acknowledgements
Financial support from the 2009SGR-1292, MAT-2007-61629 and BioTiNet research projects
