Computing the intrinsic grain boundary mobility tensor

TL;DR

This paper introduces a tensor-based approach to compute grain boundary mobility using atomistic simulations, revealing complex dependencies on temperature and driving force, and proposing a new shear coupling strength parameter.

Contribution

It presents the first computation of the intrinsic GB mobility tensor, including off-diagonal elements, and introduces a shear coupling strength S for better characterization.

Findings

GB mobility follows the same physical rule in shear and normal directions.

Mobility exhibits non-Arrhenius dependence on temperature and driving force.

Classical migration equations are adapted for diverse conditions.

Abstract

Grain boundary (GB) mobility has been conventionally computed as a single value; however, a recent study has suggested that GB mobility should be expressed as a tensor. In this work, by using atomistic simulations, the concept of GB mobility being applied to the shear direction was re-examined and it is found that it follows the same physical rule as the conventionally defined GB mobility based on the normal direction. The interface random walk method was then used to compute the intrinsic GB mobility tensor at the zero-driving force limit. In order to compute the off-diagonal elements of the intrinsic GB mobility tensor, a shear coupling strength S is introduced in this study, which we believe can better reflect the intrinsic characteristics of a GB for its coupling trend between the normal and shear motion than the widely used shear coupling factor. Furthermore, the effect of temperature and external driving force on the GB mobility tensor, especially on its symmetry, was systematically investigated. It is shown that the GB mobility in either the normal or shear direction can show a non-Arrhenius type dependence on the applied driving force, which is similar to the widely reported non-Arrhenius (or anti-thermal) dependence of GB mobility on temperature. Accordingly, the classical GB migration equation was adapted to describe the diverse variation of GB mobility due to changes in both temperature and driving force.