Shear-coupled grain-boundary migration dependence on normal strain/stress

In specific conditions, grain boundary (GB) migration occurs in polycrystalline materials as an alternative vector of plasticity compared to the usual dislocation activity. The shear-coupled GB migration, the expected most efficient GB based mechanism, couples the GB motion to an applied shear stress. Stresses on GB in polycrystalline materials have however seldom a unique pure shear component. This work investigates the influence of a normal strain on the shear coupled migration of a Σ13(320)[001] GB in a copper bicrystal using atomistic simulations. We show that the yield shear stress inducing the GB migration strongly depends on the applied normal stress. Beyond, the application of a normal stress on this GB qualitatively modifies the GB migration: while the Σ13(320)[001] GB shear-couples following the 110 migration mode without normal stress, we report the observation of the 010 mode under a sufficiently high tensile normal stress. Using the Nudge Elastic Band method, we uncover the atomistic mechanism of this 010 migration mode and energetically characterize it.