Stress-driven sliding of asymmetric grain boundaries

Abstract

Grain boundary (GB) deformation significantly influences the mechanical response of polycrystalline materials, yet most atomic-scale studies have focused on special coincidence site lattice (CSL) boundaries. In contrast, engineering polycrystals are typically dominated by asymmetric non-CSL GBs. In face-centered cubic (FCC) metals, these boundaries often undergo sliding with minimal migration, a process primarily mediated by step-free GB dislocations. Motivated by recent in situ atomic-resolution experiments, we use atomistic modeling to investigate stress‑driven sliding in asymmetric, non-CSL tilt GBs. Our results reveal that sliding is governed by the glide of extrinsic GB dislocations and their interactions with intrinsic ones. Despite the structural complexity of non-CSL boundaries, we identify the operative slip geometries of these extrinsic dislocations. Furthermore, we uncover a kink-pair mechanism of GB dislocation glide that acts as the primary rate-controlling step for sliding kinetics. These findings provide critical atomic-scale insights into asymmetric tilt GB deformation and establish a mechanistic foundation for understanding GB-mediated plasticity in engineering polycrystals.