Shear-coupled grain boundary (GB) migration has been evidenced as an efficient mechanism of plasticity in the absence of dislocation activity. The GB migration occurs through the nucleation and motion of disconnections. Using molecular simulations, we report a detailed study of the elementary mechanisms occurring during heterogeneous disconnection nucleation. We study the effect of a preexisting sessile disconnection in a symmetric $\mathrm{\Sigma }17\left(410\right)\left[001\right]$ tilt GB on the GB migration mechanism. Shearing this imperfect GB induces its migration and reveals a new GB migration mechanism through the nucleation of a mobile disconnection from the sessile one. Energy barriers and yield stress for the GB migrations are evaluated and compared to the migration of a perfect GB. We show that the migration of the imperfect GB is easier than the perfect one and that a sessile disconnection can operate as a source of disconnection driving the GB migration. This GB migration mechanism has been observed on two other high-angle GBs.

• Received 20 November 2018
• Revised 18 March 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.060601