A theoretical model was suggested which described the combined effects of grain boundary sliding and diffusion on strain hardening and ductility of nanocrystalline materials. Within the model, grain boundary sliding creates disclination dipoles near triple junctions, inducing high elastic stresses and resulting in pronounced strain hardening. At the same time, grain boundary diffusion partly relieves disclination stresses, thereby decreasing strain hardening. It was theoretically shown that good ductility of nanocrystalline materials could be reached due to optimization of grain boundary sliding and diffusion processes providing optimum strain hardening. The latter suppresses plastic strain instability and thus enhances tensile ductility. At the same time, with the optimum strain hardening, the applied stresses reach their critical level at which nanocrystalline materials fracture only if overall plastic strain was sufficiently large.

Enhanced Ductility of Nanomaterials through Optimization of Grain Boundary Sliding and Diffusion Processes. I.A.Ovidko, A.G.Sheinerman: Acta Materialia, 2009, 57[7], 2217-28