Stress-driven migration of deformation-distorted grain boundaries in nanomaterials

Stress-driven migration of low-angle grain boundaries (LAGBs) having deformation-distorted structures is theoretically described as a special mode of plastic deformation in nanocrystalline and ultrafine-grained materials. Equilibrium migration distances, energy and critical stress characteristics for stress-driven migration of deformation-distorted LAGBs are calculated as those depending on their structural and geometric parameters. It is theoretically revealed that deformation-distorted LAGBs tend to split under shear stresses, and these splitting processes lead to formation of new nanoscale (sub)grains. The role of migrating, deformation-distorted LAGBs in diminishing grain size in ultrafine-grained metallic materials during severe plastic deformation is discussed. Also, widening of deformation-distorted LAGBs in the absence of external stresses is theoretically described. Generalization of the suggested model to the case of high-angle grain boundaries is discussed. The results of our theoretical examination are compared with the corresponding experimental data and computer simulations reported in the literature.