Disconnections kinks and competing modes in shear-coupled grain boundary migration

The response of small-grained metals to mechanical stress is investigated by a theoretical study of the elementary mechanisms occurring during the shear-coupled migration of grain boundaries (GB). Investigating a model $\mathrm{\ensuremath{\Sigma}}17(410)$ GB in a copper bicrystal, both $\ensuremath{\langle}110\ensuremath{\rangle}$ and $\ensuremath{\langle}100\ensuremath{\rangle}$ GB migration modes are studied focusing on both the structural and energetic characteristics. The minimum energy paths of these shear-coupled GB migrations are computed using the nudge elastic band method. For both modes, the GB migration occurs through the nucleation and motion of disconnections. However, the atomic mechanisms of both modes qualitatively differ: While the $\ensuremath{\langle}110\ensuremath{\rangle}$ mode presents no metastable state, the $\ensuremath{\langle}100\ensuremath{\rangle}$ mode shows multiple metastable states, some of them evidencing some kinks along the disconnection lines. Disconnection kinks nucleation and motion activation energies are evaluated. Besides, the activation energies of the $\ensuremath{\langle}100\ensuremath{\rangle}$ mode are smaller than those of the $\ensuremath{\langle}110\ensuremath{\rangle}$ one except for very high stresses. These results significantly improve our knowledge of the GB migration mechanisms and the conditions under which they occur.