Kinetic and Equilibrium Shapes of Cylindrical Grain Boundaries

TL;DR

This study combines molecular dynamics and a disconnection model to analyze how cylindrical grains in nickel evolve shape, rotate, and migrate under forces, revealing the roles of boundary mobility, misorientation, and disconnection flow.

Contribution

It introduces a combined simulation and continuum model approach to predict shape evolution, rotation, and migration of cylindrical grains in nickel, highlighting disconnection flow mechanisms.

Findings

Faceted shapes form at certain misorientations.

Grain rotation depends on initial misorientation and growth direction.

Predictions align with molecular dynamics results.

Abstract

In this work, we investigate the shape evolution of rotated, embedded, initially cylindrical grains (with [001] cylinder axis) in Ni under an applied synthetic driving force via molecular dynamics simulations and a continuum, disconnection-based grain boundary migration model. For some initial misorientations, the expanding grains form well-defined, faceted shapes, while for others the shapes remain cylindrical. The embedded grains tend to rotate during grain boundary migration, with the direction of rotation dependent on initial misorientation and direction of growth (expand/shrink). The kinetic shapes, which are bounded by low mobility grain boundary planes, differ from equilibrium shapes (bounded by low energy grain boundaries). The multi-mode disconnection model-based predictions are consistent with the molecular dynamics results for faceting tendency, kinetic grain shape, and grain rotation as a function of misorientation and whether the grains are expanding or contracting. This demonstrates that grain boundary migration and associated grain rotation are mediated by disconnection flow along grain boundaries.