CROSSOVER FROM DISLOCATION SLIP TO DEFORMATION TWINNING IN NANOSTRUCTURED AND COARSE-GRAINED METALS

A theoretical model is suggested which describes crossover from dislocation slip to deformation twinning in nanostructured and coarse-grained polycrystalline metals. In the framework of the suggested model, lattice dislocations that mediate dislocation slip in a grain interior are stopped by a grain boundary and form a pile-up configuration. Head dislocations of the pile-up are absorbed by the grain boundary where they split into grain boundary dislocations. A deformation twin is nucleated at these grain boundary dislocations and propagates to the neighbouring grain interior. The energy and stress characteristics of this transformation in nanostructured and coarse-grained polycrystalline metals (Ni, Ti) are calculated. Results of the suggested theoretical model are consistent with experimental data reported in literature.