Effect of Anisotropic Peierls Barrier on the Evolution of Discrete Dislocation Networks in Ni

TL;DR

This study uses discrete dislocation dynamics simulations to explore how elastic anisotropy and Peierls stress influence dislocation network evolution and plasticity in single crystal Ni, revealing complex interactions between dislocation character and mechanical response.

Contribution

It demonstrates the impact of anisotropic Peierls barriers on dislocation network evolution and plasticity, introducing a superposition model for predicting hardening behavior.

Findings

Suppression of plasticity in nearly screw dislocation segments.

Increased screw Peierls stress raises initial strain hardening rate.

Networks tend to maintain connectivity with unequal Peierls stress.

Abstract

Over low and intermediate strain rates, plasticity in face centered cubic (FCC) metals is governed by the glide of dislocations, which manifest as complex networks that evolve with strain. Considering the elastic anisotropy of FCC metals, the characteristics of dislocation motion are also anisotropic (i.e., dislocation character angle-dependent), which is expected to notably influence the overall evolution of the dislocation network, and consequently, the plastic response of these materials. The aggregate influence of the anisotropy in the Peierls stress on the mechanical response of single crystal Ni was investigated in the present work using discrete dislocation dynamics simulations. Twenty initial dislocation networks, differing in their configuration and dislocation density, were deformed under uniaxial tension up to at least 0.9% strain, and the analysis of character-dependent dynamics showed a suppression of plasticity only for segments of nearly screw character. While the increased screw component of the Peierls stress raised the initial strain hardening rate, it also resulted in longer dislocation segments overall, contrary to the reasoning that longer pinned segments exhibit a lower resistance to motion and might give a weaker response. A non-linear superposition principle is demonstrated to predict the hardening reasonably well, considering the cumulative effects of forest and Peierls stress-related strengthening. Further analysis of the network topology revealed a tendency to maintain connectivity over the course of deformation for those networks simulated using an unequal Peierls stress. The general increases in hardening rate and network connectivity contrast with the localized reduction of dislocation motion, which occurred mainly for segments of nearly screw-type character.