Three-Level Model for Description of Polycrystal Superplastic Deformation

We proposed a modified statistical multilevel model based on crystal plasticity, which allows describing deformation of polycrystalline metals with transition to structural superplasticity regime. The main mechanisms of plastic and superplastic deformation are taken into account: intragranular dislocation sliding, crystallite lattice rotations, grain structure evolution; particular attention is paid to the description of grain boundary sliding, leading in structural superplasticity regime and transition to it, and accompanying accommodation mechanisms - grain boundary diffusion and dynamic recrystallization. The model takes into account interaction of grain-boundary and intragranular sliding: influx of intragranular dislocations into the boundary makes it more defective (nonequilibrium), increases the boundary energy and promotes grain-boundary sliding; in turn, grain-boundary sliding leads to decrease in defects in the boundary and, as a consequence, to reducing the resistance to intragranular sliding. The results of numerical calculations for uniaxial loading are in satisfactory agreement with the experimental ones. The processes of complex loading are investigated. The role of main mechanisms is defined and analyzed during deformation.