This document summarizes research on the mechanical behavior of a Zr-based metallic glass under indentation. Nanoindentation and microindentation experiments were conducted to characterize the material's properties at different length scales. Finite element modeling using Mohr-Coulomb criteria was also used to model the microscale indentation. The results show a significant reduction in modulus with increasing indentation depth, which is attributed to shear band formation that damages the material. Ongoing work aims to develop a constitutive model that captures this damage effect.

1. Mechanical behaviour of Zr‐based
metallic glass in indentation
Presented By: Vaibhav Phadnis
Vahid Nekouie
Gayan Abeygunawardane‐Arachchige
Anish Roy
Vadim Silberschmidt
Wolfson School of Mechanical & Manufacturing Engineering, Loughborough University
Uta Kühn
IFW/Dresden
1

2. Introduction & Motivation
 Metallic glass shows unique mechanical properties
 Evidence of length scale effects
 Deformation mechanisms of metallic glass are unique
 plastic shear flow in the microscale, but brittle fracture in macroscale
 deformation induced ductilization
 Ultimate goal is to predict component deformation
under macroscopically homogeneous loads
2

3. BMG Material
BMG alloy manufactured at IFW/Dresden
Zr48Cu36Al8Ag8
Samples: 70 mm × 10 mm × 2 mm ; 40 mm × 30 mm × 1.5 mm
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Outline:
 Mechanical characterisation of the BMG alloy
 Macroscale
 Microscale
 Nanoscale
 Constitutive material modelling and Finite Element
Analysis

4. Macroscale
 Bending Tests
 Elastic Modulus
 Poisson’s ratio
 DMA
4
E [GPa] ν Tg [°C]
In‐house experiments 80 – 86 0.34 – 0.35 425 ± 3
Date from IFW 98 – 102 430 ± 3
Literature 115 417

5. 5ISMANAM 2013
Crystalline phase
XRD results show :
(i) The structure of the metallic glass is not completely amorphous.
(ii) There are crystalline phases in the materials and these phases are not
uniformly dispersed in the materials.
Macroscale
 XRD
Crystalline phase

6. 6
Nano/Micro Test (Micro Materials Ltd.)
Tests performed:
 Nano and Micro‐indentation
 Load rate: (0.1, 1, 2,10 mN/s)
 Cyclic loading
Spherical Indenter
Micro: r = 50 μm
Nano: r = 5 μm
Nano‐Micro indentation studies
Sample is cut Polished Zygo Talisurf
Ra = 2 to 3 nm

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Nanoindentation
Loading Rate = 0.1 mN/sec
Cyclic loading was performed to determine initiation of plastic deformation (pop‐in)
Load = 2 mN
Fully Elastic deformation
Load = 3 mN
Initiation of plasticity

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Nanoindentation
Loading Rate = 0.1 mN/sec
Cyclic loading was performed to determine initiation of plastic deformation (pop‐in)
Pop‐in

9. Nanoindentation

10. 10
Nanoindentation
130 mN 190 mN 220 mN
Maximum load 275 mN
220 mN
190 mN
130 mN

11. 11
Microindentation
Load/partial unload technique
3 cycles of loading‐unloading
Max load = 15 N
Loading rates = 1 mN/s, 2 mN/s and 10 mN/s,

12. Microindentation: SEM
Load < 10 N
No shear bands visible
12

13. 13
10 mN/s
1 mN/s
Microindentation: SEM

14. 14
Indentation Depth (µm) Reduced Modulus (GPa) Young modulus (GPa) Hardness (GPa)
1.1 87 82 4.81
1.5 90 86 5.22
1.8 88 84 5.07
2.3 95 90 5.56
Microindentation results
Properties
Cycle Indentation depth
(m)
Reduced Modulus
(GPa)
Young modulus
(GPa)
1 6.2 54 47
2 12.5 50 43.5
3 19.4 46 40.02
Load rate 1 mN/s Load rate 2 mN/s
Cycle Indentation depth
(m)
Reduced Modulus
(GPa)
Young modulus
(GPa)
1 6.2 48 41.7
2 12.1 40 34.8
3 18.2 38 33.06
Nanoindentation results
Load rate 10 mN/s
Cycle Indentation depth
(m)
Reduced Modulus
(GPa)
Young modulus
(GPa)
1 5.7 48.03 41.8
2 10.6 39.8 34.6
3 15.3 36.2 31.5

15. MODELLING OF INDENTATION
/Finite Element Modelling
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16. Microscale modelling
 Mohr‐Coulomb: hydrostatic stress component is considered.
 the normal stress component on the shear plane is important!
MSC Marc 2012 is used to model
Linear MC criterion is used:
/
Here: and
To calculate, and /
:
/
and sin
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17. 17
Spherical Indenter Radius: 50 μm
FE Model Dimension: (90 × 90 × 100) µm
Displacement Given to Indenter: 4 µm to 10 µm
Initial # of Elements: 4000
Element type: Eight noded hex elements (Type 7)
Spherical Indenter: Analytical Rigid Body
Local Adaptive remeshing: Nodes Within a Box, Cylinder or Sphere Criterion
FE model
Quarter Model, use of symmetry planes
BC: bottom rigid
High Performance Computing – Hydra Cluster
• 161 Computer nodes.
• 1956 core 64 bit Intel Xeon cluster.
• Each having two 6‐core Intel Westmere Xeon X5650 CPUs + 24GB of memory.
• Time taken to finish the Analysis: 2 Hours
• Number of cores – 12.

18. 18
Shear Stress Variation Normal Stress Variation
FE model: Results
End of Loading End of Unloading

19. 19
FE model: Results
E (GPa) σ' (MPa) µ α
38 1500 0.2 0.02

20. Outlook: Why is there such a significant reduction in Modulus?
 Shear bands ‘break up’ the amorphous material into islands of amorphous MG
 The shear bands help ‘slip’ these islands under macroscopic loads
 This will reduce the reaction force on the indenter ►reduced stiffness from experiments
 Material Damage needs to be characterised [in macroscopic modelling]
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21. Outlook
 MC model is not appropriate for the BMG under study
 The process of deformation induces damage in the
material.
 This damage needs to be characterised in the
constitutive behaviour of the material.
 A gradient plasticity based approach is currently being
developed to capture the effect of the local shear bands
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22. Indentation Profile: Cycle 1 loading‐unloading
22
Distance from the Indentor Axis (μm)
Indentation Depth (μm)
‐12
‐10
‐8
‐6
‐4
‐2
0
2
4
0 10 20 30 40 50 60 70 80
Indentor at Full displacement
Indentor Fully Extracted