Thickness-Dependent Strain Rate Sensitivity of Nanolayers via the Nanoindentation Technique

Jian Song,Zhe Fan,Yue Liu,Xinghang Zhang

doi:10.3390/cryst8030128

Jian Song, Zhe Fan + Show 2 more

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https://doi.org/10.3390/cryst8030128

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Abstract

The strain rate sensitivity (SRS) and dislocation activation volume are two inter-related material properties for understanding thermally-activated plastic deformation, such as creep. For face-centered-cubic metals, SRS normally increases with decreasing grain size, whereas the opposite holds for body-center-cubic metals. However, these findings are applicable to metals with average grain sizes greater than tens of nanometers. Recent studies on mechanical behaviors presented distinct deformation mechanisms in multilayers with individual layer thickness of 20 nanometers or less. It is necessary to estimate the SRS and plastic deformation mechanisms in this regime. Here, we review a new nanoindentation test method that renders reliable hardness measurement insensitive to thermal drift, and its application on SRS of Cu/amorphous-CuNb nanolayers. The new technique is applied to Cu films and returns expected SRS values when compared to conventional tensile test results. The SRS of Cu/amorphous-CuNb nanolayers demonstrates two distinct deformation mechanisms depending on layer thickness: dislocation pileup-dominated and interface-mediated deformation mechanisms.

Highlights

The plastic deformation can be regarded as a thermally-activated process which can be quantitatively characterized by the values of the strain rate sensitivity (SRS), m, and the dislocation activation volume, V* [1,2]
The values of SRS are strongly size-dependent: for face-centered-cubic metals, SRS normally increases with decreasing grain sizes, whereas the opposite holds for body-center-cubic structures [3]
The new method is applied in two model systems to reduce the thermal drift effect and yields reliable results

Summary

Introduction

The plastic deformation can be regarded as a thermally-activated process which can be quantitatively characterized by the values of the strain rate sensitivity (SRS), m, and the dislocation activation volume, V* [1,2]. SRS is an important indicator of the plasticity of metallic materials, which can be estimated by the amount of activation volume required for dislocation motions. These two inter-related material properties are important for understanding thermally-activated plastic deformation, such as creep. For crystalline metals, higher values of SRS are often accompanied by excellent ductility and deformability. Metallic glasses (MGs) exhibit high strength, excellent abrasion and corrosion resistance [4], but they are generally brittle due to the shear band (SB)

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Discussion

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