Length scales and scale-free dynamics of dislocations in dense solid solutions

TL;DR

This study investigates how dislocations in dense solid solutions behave under stress and temperature, revealing a depinning transition characterized by a diverging correlation length and proposing a physical model to explain the length-dependent dislocation mobility.

Contribution

The paper introduces a new physical model for dislocation behavior in solid solutions, highlighting the depinning transition and addressing gaps in existing strengthening theories.

Findings

Dislocation roughness exhibits two regimes separated by a correlation length.

The correlation length diverges at the critical depinning stress.

A physical model based on coherent line bowing explains the observed phenomena.

Abstract

The fundamental interactions between an edge dislocation and a random solid solution are studied by analyzing dislocation line roughness profiles obtained from molecular dynamics simulations of Fe0.70Ni0.11 Cr0.19 over a range of stresses and temperatures. These roughness profiles reveal the hallmark features of a depinning transition. Namely, below a temperature-dependent critical stress, the dislocation line exhibits roughness in two different length scale regimes which are divided by a so-called correlation length. This correlation length increases with applied stress and at the critical stress (depinning transition or yield stress) formally goes to infinity. Above the critical stress, the line roughness profile converges to that of a random noise field. Motivated by these results, a physical model is developed based on the notion of coherent line bowing over all length scales below the correlation length. Above the correlation length, the solute field prohibits such coherent line bow outs. Using this model, we identify potential gaps in existing theories of solid solution strengthening and show that recent observations of length-dependent dislocation mobilities can be rationalized.