Grain Boundary Shear Coupling is Not a Grain Boundary Property

TL;DR

This paper demonstrates through MD simulations and theory that grain boundary shear coupling varies with external conditions and is not an inherent property of the boundary itself.

Contribution

The authors develop a microscopic statistical theory for grain boundary migration based on disconnections, explaining the dependence of shear coupling on external driving forces and temperature.

Findings

Shear coupling depends on driving force type and magnitude.

The proposed theory quantitatively matches MD simulation results.

Shear coupling is not an intrinsic grain boundary property.

Abstract

Shear coupling implies that all grain boundary (GB) migration necessarily creates mechanical stresses/strains and is a key component to the evolution of all polycrystalline microstructures. We present MD simulation data and theoretical analyses that demonstrate the GB shear coupling is not an intrinsic GB property, but rather strongly depends on the type and magnitude of the driving force for migration and temperature. We resolve this apparent paradox by proposing a microscopic theory for GB migration that is based upon a statistical ensemble of line defects (disconnections) that are constrained to lie in the GB. Comparison with the MD results for several GBs provides quantitative validation of the theory as a function of stress, chemical potential jump and temperature.