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Flow stress, strain hardening rate, and dislocation avalanches: Size and strain rate dependence in nano- and micro-scaled single crystal Tungsten

Abstract

The plastic behavior of body centered cubic metals generally exhibits strong strain rate and size dependence, attributed to the mobility of dislocations and availability of dislocation sources. Through in situ scanning electron microscope nano-compression testing on room temperature Tungsten single crystal micro- and nano- pillars with diameters ranging from 2000 nm to 100 nm, this work demonstrates the coupled effect of size and strain rate on plastic flow behavior. It is found that strain rate sensitivity of flow stress decreases with decreasing size, with 100 nm pillars showing negative strain rate sensitivity. Accordingly, the size effect decreases with increasing strain rate. In addition, the strain hardening rate demonstrates strong size dependence and statistically insignificant strain rate dependence, increasing with more scatter at different strain rate as size decreases. We further show the influence of size and strain rate on pillar morphology, where smaller pillars and lower strain rates are dominated by localized plastic deformation.

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