Athermal grain growth through cooperative migration of grain boundaries in deformed nanomaterials

A special mode of both athermal grain growth and associated plastic deformation in nanocrystalline metals and ceramics is theoretically described. The mode represents the stress-induced cooperative migration of grain boundaries when the migration involves two or more neighboring boundaries. We calculated two critical external stress levels attributed to the start of migration of two neighboring boundaries and their meeting, respectively. After their convergence, grain boundaries can annihilate, stop, move together or move in opposite directions, depending on their characteristics.