Dual migration modes of unfaulted disconnections on curved twin boundaries

TL;DR

This study uncovers two distinct migration modes of unfaulted disconnections on twin boundaries in aluminum, showing how core structure influences migration behavior and kinetics through molecular dynamics simulations.

Contribution

It reveals the fundamental impact of disconnection core structure on migration mode and kinetics, advancing understanding of grain boundary migration mechanisms.

Findings

Edge disconnection migrates via double-kink mechanism with temperature-dependent velocity.

Screw dipole disconnection exhibits lower energy barrier and stochastic bidirectional motion.

Core structure determines the migration mode and kinetic behavior of disconnections.

Abstract

Grain boundary migration governs microstructural evolution in crystalline materials, directly influencing mechanical properties such as strength and thermal stability. Disconnections, which are line defects formed at grain boundaries in response to local curvature, have been identified as critical carriers of boundary migration. Here, we investigate the glide of unfaulted disconnections (UFDs) on a coherent twin boundary in aluminum at elevated temperatures using molecular dynamics simulations combined with the Nudged Elastic Band (NEB) method. Our results reveal a striking bifurcation in migration behavior depending on the disconnection core structure. UFDs with a pure edge Burgers vector migrate via a thermally activated double-kink mechanism, exhibiting a migration velocity that increases monotonically with temperature. In contrast, UFDs containing a screw dipole component possess an energy barrier approximately eight times lower, and their core structure undergoes a continuous transformation during glide, giving rise to stochastic, bidirectional motion with no systematic temperature dependence. These findings demonstrate that the disconnection core structure fundamentally dictates the migration mode and kinetics of twin boundaries, offering new mechanistic insights into disconnection-mediated grain boundary migration.