Optimum grain size for superplastic deformation

The conditions of structural superplasticity under which the optimum grain size in materials deformed were analyzed. Superplasticity is the ability of poly-crystalline fine-grained materials to exhibit high plasticity which is manifested by considerable elongations under tensile testing. The usual conditions for the superplasticity manifestation are elevated temperatures and a relatively low strain rate whose value is inversely proportional to the square of the grain size. It is necessary to provide conditions, in order to realize GBS(grain boundary sliding) under which the grain-boundary slip and accommodation of this slip in triple junctions take place. A necessary condition for the appearance of the self-GBS is the transition of grain boundaries into a nonequilibrium state caused by their interaction with the flow of lattice dislocations bombarding the boundaries in the course of intragranular deformation.