Misfit-dislocation hierarchy governs sliding of asymmetric non-CSL grain boundaries

Abstract

Grain boundary (GB) deformation significantly influences the mechanical response of polycrystalline materials, yet most atomistic studies have focused on coincidence site lattice (CSL) boundaries. Motivated by in situ atomic-resolution observations, we investigate step-free sliding along asymmetric non-CSL tilt GBs in face-centered cubic (FCC) metals using atomistic modeling. In these incommensurate GBs, a dense array of primary misfit dislocations accommodates the local interfacial mismatch, whereas a more widely spaced array of secondary GB misfit dislocations accommodates the residual mismatch. Uniform sliding calculations reveal two distinct quantities: the minimum GB structural periodicity λ, defined by the repeating arrangement of primary GB misfit dislocations, and the slip vector b, determined by the minimum displacement-shift-complete translation that restores an equivalent GB structure. Nonuniform sliding proceeds through the glide of secondary GB misfit dislocations, which carry b and transform successive boundary segments between crystallographically equivalent translation states. These secondary misfit dislocations dissociate into partials, each carrying a partial Burgers vector b_p and connecting intermediate interfacial states. The characteristic spacing between secondary misfit partials defines a longer periodicity Λ. Below the athermal stress, each partial glides through a two-step thermally activated kink-pair mechanism, advances the partial by one structural period l. These results establish a unified crystallographic and dislocation-based framework for understanding stress-driven sliding in structurally complex asymmetric GBs.