Disclination mediated plasticity in shear-coupled boundary migration

The shear-coupled boundary migration of 〈0 0 1〉 symmetric tilt boundaries is investigated within the framework of an elasto-plastic theory of disclination and dislocation fields. The tilt boundaries are built from periodic partial wedge-disclination dipole arrays, on the basis of their atomistic topography. Non-locality of the elastic response of the adjacent crystals stems from the defected structure of their boundary. Upon applying a shear strain to the bicrystal, couple stresses are generated, which set the disclination dipole array into motion normal to the boundary. In the process, edge dislocation densities with partial Burgers vector lying along the boundary are nucleated, whose glide parallel to the boundary and annihilation produces plastic shear. The misorientation dependence of the shear coupling factor predicted by the model is in full agreement with data from atomistic simulations and experiments. It is found to depend on the polarity and the magnitude of the wedge disclination dipoles composing the grain boundary.