Atomistic mechanisms of intermittent plasticity in metals: Dislocation avalanches and defect cluster pinning

TL;DR

This study uses molecular dynamics simulations to reveal how different metals exhibit intermittent plasticity with power-law behaviors, driven by dislocation avalanches and defect pinning, with distinct mechanisms and exponents.

Contribution

It introduces a molecular dynamics approach to observe and analyze the mechanisms of intermittent plasticity and dislocation dynamics in metals, highlighting differences among Ni, Cu, and Al.

Findings

Power-law stress drop and waiting time observed in Ni, Cu, and Al.

Dislocation avalanches cause power-law behavior in Cu and Ni.

Dislocation pinning mechanism in Al leads to different power-law exponents.

Abstract

Intermittent plastic deformation in crystals with power-law behaviors has been reported in previous experimental studies. The power-law behavior is reminiscent of self-organized criticality, and mesoscopic models have been proposed that describe this behavior in crystals. In this letter, we show that intermittent plasticity in metals under tensile deformation can be observed in molecular dynamics models, using embedded atom method potentials for Ni, Cu, and Al. Power-law behaviors of stress drop and waiting time of plastic deformation events are observed. It is shown that power-law behavior is due to dislocation avalanche motions in Cu and Ni. A different mechanism of dislocation pinning is found in Al. These different stress relaxation mechanisms give different power-law exponents. We propose a probabilistic model to describe the novel dislocation motion in Al, and analytically deduce the power-law behavior.