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Research Papers

Effect of Interfaces in the Work Hardening of Nanoscale Multilayer Metallic Composites During Nanoindentation: A Molecular Dynamics Investigation

[+] Author and Article Information
S. Shao

e-mail: shuai.shao@email.wsu.edu

H. M. Zbib

e-mail: zbib@wsu.edu

I. Mastorakos

e-mail: mastorakos@wsu.edu

D. F. Bahr

e-mail: dbahr@wsu.edu
School of Mechanical and Materials Engineering,
Washington State University,
Pullman, WA 99164

Contributed by the Materials Division of ASME for publication in the Journal of Engineering Materials and Technology. Manuscript received October 25, 2011; final manuscript received April 12, 2012; published online March 25, 2013. Assoc. Editor: Hamid Garmestani.

J. Eng. Mater. Technol 135(2), 021001 (Mar 25, 2013) (8 pages) Paper No: MATS-11-1238; doi: 10.1115/1.4023672 History: Received October 25, 2011; Revised April 12, 2012

To study the strain hardening in nanoscale multilayer metallic (NMM) composites, atomistic simulations of nanoindentation are performed on CuNi, CuNb, and CuNiNb multilayers. The load-depth data were converted to hardness-strain data that were then modeled using power law. The plastic deformation of the multilayers is closely examined. It is found that the strain hardening in the incoherent CuNb and NiNb interfaces is stronger than the coherent CuNi interface. The hardening parameters are discovered to be closely related to the density of the dislocations in the incoherent interfaces, which in turn is found to have power law dependence on two length scales: indentation depth and layer thickness. Based on these results, a constitutive law for extracting strain hardening in NMM from nanoindentation data is developed.

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Figures

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Fig. 1

Simulation setup of the nanoindentations in this work

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Fig. 2

Load depth curves and plastic portion of the converted hardness-strain curves of CuNi, CuNb, and CuNiNb multilayers. Individual layer thickness h = 30Å, indenter radius R = 90Å.

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Fig. 3

The variation of K* (a)–(c) and n* (d)–(f) with respect to individual layer thickness. The different graphs ((a)–(c) and (d)–(f)) show this variation under different indenter radii: ((a) and (d)) for R = 60Å, ((b) and (e)) for R = 90Å and ((c) and (f)) for R = 150Å. Error bars represent 95% confidence bounds.

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Fig. 4

Snapshots of atomistic configurations of CuNi ((a)–(c)), CuNb ((e)–(g)), and CuNiNb ((h)–(j)) configures with variable individual layers thickness (20Å, 30Å, and 50Å) at indentation depth of 20Å; the indenter radius used in this figure is 90Å. Other simulations using larger indenter are not shown for brevity. In this figure, atomic defects, e.g., dislocation lines, incoherent interfaces are detected using centro-symmetry parameter (CSP) [30]. Atoms are colored as following to indentify fcc interfaces: red for Cu, blue for Ni, and yellow for Nb. The dislocation lines in fcc layers are all Shockley partial dislocations; the stacking faults are not shown for better visibility.

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Fig. 5

(a) Plot of ρi(27Å) versus interfacial number i. (b) Plot of ρ¯ versus individual layer thickness h, for d = 27Å

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Fig. 6

Plots of exponent n* versus total interfacial shear ρ¯(d) (left) and prefactor K* versus total interfacial shear ρ¯(d). Where d = 27Å is taken.

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Fig. 7

Snapshots of atomistic configurations of CuNiNb (a) and NiCuNb (b) indented by an indenter with radius R = 90Å at depth d = 20Å

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Fig. 8

Demonstration of the hardening effect of CuNi, CuNb, and CuNiNb interfaces with the variation of ρ¯(d). Here d = 27Å is taken as an example as before.

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Fig. 9

Plot of ρ¯(d) versus h*/R when d = 27Å

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