Complexity of disconnection dynamics during grain boundary migration

The Interfacial Line Defect Analysis (ILDA) method is used to fully resolve the time-evolving disconnection network governing migration of the Σ 5(210)[001] symmetric-tilt grain boundary in Al. Rather than proceeding by smooth glide of largely straight disconnections, as assumed in most theories and observed in prior works, interface migration occurs through a reaction-dense network of transient defect activity. A “flickering” mechanism is identified in which smaller loops repeatedly nucleate, fluctuate, and annihilate, leading to boundary translation through pure step deposition. Such flickering also gives rise to topologically complex configurations involving disconnections of multiple step heights which we term mixed-step complexes. The one glissile disconnection that is observed is seen to migrate via a unique dissociation-based mechanism that differs from the traditional kink-pair mechanism. Finally, the shear-coupling response is seen to be intimately tied to the instantaneous defect densities and their activity.