Properties of dislocation lines in crystals with strong atomic-scale disorder

TL;DR

This paper investigates the behavior of dislocation lines in crystals with strong atomic-scale disorder, revealing how disorder affects dislocation dynamics, line tension, and flow stress predictions, especially relevant for high entropy alloys.

Contribution

It introduces a discrete dislocation dynamics approach to analyze dislocation motion under strong stochastic forces, accounting for corrections to scaling in highly disordered materials.

Findings

Dislocation wandering under thermal forces can be exactly modeled with a linear stochastic differential equation.

Effective line tension depends on scale and can be deduced from Fourier modes of the dislocation line.

Pinning length serves as a predictor for flow stress in disordered crystals.

Abstract

We use a discrete dislocation dynamics (DDD) approach to study the motion of a dislocation under strong stochastic forces that may cause bending and roughening of the dislocation line on scales that are comparable to the dislocation core radius. In such situations, which may be relevant in high entropy alloys (HEA) exhibiting strong atomic scale disorder, standard scaling arguments based upon a line tension approximation may be no longer adequate and corrections to scaling need to be considered. We first study the wandering of the dislocation under thermal Langevin forces. This leads to a linear stochastic differential equation which can be exactly solved. From the Fourier modes of the thermalized dislocation line we can directly deduce the scale dependent effective line tension. We then use this information to investigate the wandering of a dislocation in a crystal with spatial, time-independent ('quenched') disorder. We establish the pinning length and show how this length can be used as a predictor of the flow stress. Implications for the determination of flow stresses in HEA from molecular dynamics simulations are discussed.