| Stress-driven formation of nanograin chains - groups of two or more elongated nanograins - in nanocrystalline (NC) and ultrafine-grained (UFG) materials is theoretically described. Within the suggested theoretical description, stress-driven formation of new nanograins is enhanced at previously generated nanograins with disclinations at their grain boundary junctions. The formation process occurs through splitting transformations of grain boundaries (containing disclination dipoles) into immobile and mobile grain boundaries. Stress-driven migration of mobile grain boundaries serves as a plastic flow mode at the nanograin level and results in formation of nanograin chains. It is shown that the transformations under consideration are energetically favorable in mechanically loaded nanoceramics α-Al2O3 (sapphire) and NC/UFG Al (aluminum) in certain ranges of their parameters. |
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