Why Grain Growth is Not Curvature Flow

TL;DR

This paper challenges the traditional view of grain growth as a simple curvature-driven process, showing that shear coupling significantly influences grain boundary migration, which is supported by large-scale simulations and experimental observations.

Contribution

It reveals that shear deformation coupled with grain boundary motion causes deviations from classical curvature flow models, providing a more accurate framework for microstructure evolution prediction.

Findings

Shear coupling significantly affects grain boundary migration.

Classical curvature flow models are insufficient for realistic grain growth.

Simulations align with recent experimental observations.

Abstract

Grain growth in polycrystals is traditionally considered a capillarity-driven process, where grain boundaries (GBs) migrate toward their centers of curvature (i.e., mean curvature flow) with a velocity proportional to the local curvature (including extensions to account for anisotropic GB energy and mobility). Experimental and simulation evidence shows that this simplistic view is untrue. We demonstrate that the failure of the classical mean curvature flow description of grain growth mainly originates from the shear deformation naturally coupled with GB motion (i.e., shear coupling). Our findings are built on large-scale microstructure evolution simulations incorporating the fundamental (crystallography-respecting) microscopic mechanism of GB migration. The nature of the deviations from curvature flow revealed in our simulations is consistent with observations in recent experimental studies on different materials. This work also demonstrates how to incorporate the mechanical effects that are essential to the accurate prediction of microstructure evolution.