Theory and Simulation of the diffusion of kinks on dislocations in bcc metals

TL;DR

This paper combines molecular dynamics simulations and a discrete Frenkel-Kontorova-Langevin model to analyze the thermally activated diffusion of kinks on dislocations in bcc iron, revealing key energy barriers and the role of discreteness effects.

Contribution

It introduces a novel multiscale approach linking MD simulations with a simplified FKL model to study dislocation kink dynamics in bcc metals.

Findings

Kink formation energy and migration barriers are quantified.

Discreteness effects are crucial in thermally activated dislocation glide.

The model predicts dislocation behavior under low-stress conditions.

Abstract

Isolated kinks on thermally fluctuating (1/2)<111> screw, <100> edge and (1/2)<111> edge dislocations in bcc iron are simulated under zero stress conditions using molecular dynamics (MD). Kinks are seen to perform stochastic motion in a potential landscape that depends on the dislocation character and geometry, and their motion provides fresh insight into the coupling of dislocations to a heat bath. The kink formation energy, migration barrier and friction parameter are deduced from the simulations. A discrete Frenkel-Kontorova-Langevin (FKL) model is able to reproduce the coarse grained data from MD at a fraction of the computational cost, without assuming an a priori temperature dependence beyond the fluctuation-dissipation theorem. Analytic results reveal that discreteness effects play an essential r\^ole in thermally activated dislocation glide, revealing the existence of a crucial intermediate length scale between molecular and dislocation dynamics. The model is used to investigate dislocation motion under the vanishingly small stress levels found in the evolution of dislocation microstructures in irradiated materials.