Cooperative grain boundary sliding and nanograin nucleation process in nanocrystalline, ultrafine-grained, and polycrystalline solids

A special physical mode of plastic deformation in nanocrystalline, ultrafine-grained, and polycrystalline solids is suggested and theoretically described. The mode represents the cooperative grain boundary (GB) sliding and nanoscale grain nucleation (occurring through stress-driven splitting and migration of GBs) process. It is theoretically revealed that, in certain ranges of parameters of the defect structure under consideration, the special deformation mode is more energetically favorable than both pure GB sliding and the previously examined [Bobylev et al., Phys. Rev. Lett. 105, 055504 (2010)] cooperative GB sliding and migration process. In addition, the special deformation mode enhances ductility of nanocrystalline and ultrafine-grained solids, and this enhancing effect is more pronounced compared to that of the cooperative GB sliding and migration process.