Role Of Sessile Disconnection Dipoles In Shear-Coupled Grain Boundary Migration

Shear-coupled grain boundary (GB) migration has been evidenced as an effective plastic mechanism in absence of the usual intragranular dislocation activity. GB migration occurs through the nucleation and further motion of disconnections. For perfect GBs, the activation barrier for migration is dominated by the disconnection nucleation. In this study, we examine the effects of a dipole of sessile disconnections on the shear-coupled GB migration using molecular dynamics simulations on a Sigma 41[001] (540) symmetric tilt GB in aluminum. The first effect is observed on disconnection nucleation: we show that the disconnection dipole can operate as a source of mobile disconnections. The corresponding yield stress is weakly affected, but the GB migration energy barrier can be reduced by 35%. The second effect is seen on the disconnection mobility: the sessile disconnection dipole impedes the disconnection motion by repulsing or attracting it. We conclude that the influence of such dipole on the GB migration favors the nucleation of mobile disconnections on one hand but slows down their motion on the other hand.