Atomistic deformation behavior of single and twin crystalline Cu nanopillars with preexisting dislocations

TL;DR

This study uses molecular dynamics simulations to explore how preexisting dislocations and twin boundaries influence the plastic deformation of copper nanopillars, revealing size-dependent behaviors and dislocation interactions.

Contribution

It provides new insights into the role of initial dislocation sources and twin boundaries in nanopillar deformation, linking dislocation length to yield stress.

Findings

Yield stress correlates inversely with the longest dislocation length.

Twin boundaries act as pinning surfaces reducing dislocation starvation.

Size effects influence the mechanical response and dislocation behavior.

Abstract

Molecular dynamics simulations are performed to investigate the role of a coherent {\Sigma}3 (111) twin boundary on the plastic deformation behavior of Cu nanopillars. Our work reveals that the mechanical response of pillars with and without the twin boundary is decisively driven by the characteristics of initial dislocation sources. In the condition of comparably large pillar size and abundant initial mobile dislocations, overall yield and flow stresses are controlled by the longest, available mobile dislocation. An inverse correlation of the yield and flow stresses with the length of the longest dislocation is established, and its extrapolation agrees well with experimental yield stress data. The experimentally reported subtle differences in yield and flow stresses between pillars with and without the twin boundary are thus likely related to the maximum lengths of the mobile dislocations. In the condition of comparably small pillar size, for which a reduction of mobile dislocations during heat treatment and mechanical loading occurs, the mechanical response of pillars with and without the twin boundary can be clearly distinguished. Dislocation starvation during deformation is more clearly present in pillars without the twin boundary than in pillars with the twin boundary because the twin boundary acts as a pinning surface for the dislocation network.