Relative relevance of mobility and driving force on edge dislocation climb by the vacancy mechanism

TL;DR

This study investigates the factors influencing edge dislocation climb in alpha-iron, revealing that thermodynamic chemical potential differences dominate over stress-induced effects, with implications for atomistic simulation accuracy.

Contribution

The paper demonstrates that vacancy chemical potential differences are the primary driver of dislocation climb in alpha-iron, despite stress effects on migration barriers being present but less influential.

Findings

Thermodynamic chemical potential differences dominate dislocation climb.

Stress modifies migration barriers but has minimal impact on mobility.

Dislocation climb is hindered by small chemical potential differences.

Abstract

In this work we examine the driving force for edge dislocations to climb in $\alpha$-Fe from atomistic and mesoscale viewpoints. We study the bias for the climb process depending on the dislocation orientation and the applied stress as coming from both the gradient of the chemical potential and the transport coefficients. Both terms are modified by the applied stress and therefore contribute to climb. Surprisingly, even though the vacancy migration barrier distribution is modified by the external stress as obtained by nudged-elastic band calculations, the mobilities resulting from a kinetic Monte Carlo model applied on the obtained energy landscape are indistinguishable, independently of the stress. Moreover, an object kinetic Monte Carlo (OKMC) model including the effect of the dislocation strain field to first order shows indeed a slight anisotropic component in the diffusion in more complex dislocation configurations. However, the OKMC results highlight the fact that the thermodynamic component is the dominant driving force. We conclude that in $\alpha$-Fe under thermal conditions, the main source of bias is given by the difference in vacancy chemical potentials, which is small enough to hinder the process for dynamic atomistic simulations.