Effect of cooperative grain boundary sliding and migration on crack growth in nanocrystalline solids

A new mechanism of fracture toughness enhancement in nanocrystalline metals and ceramics is suggested. The mechanism represents the cooperative grain boundary (GB) sliding and stress-driven GB migration process near the tips of growing cracks. It is shown that this mechanism can increase the critical stress intensity factor for crack growth in nanocrystalline materials by a factor of three or more and thus considerably enhances the fracture toughness of such materials.