Grain rotation dependent non-homogeneous deformation behavior in nanocrystalline materials

Many experimental observations have indicated a transition from homogeneous to non-homogeneous plastic deformation on nanocrystalline materials. Based on a grain rotation theory of diffusion-accommodated grain-boundary sliding, a new phase mixture model was developed to predict the softening of nanocrystalline materials considering non-homogeneous plastic deformation due to shear bands subjected to quasi-static rates of loading. In this phase mixture model, nanocrystalline materials were treated as composites consisting of grain interior and grain boundary phases. Grain interior phase was divided into soft-grain interior part with soft orientation and hard-grain interior part with hard orientation. The grain rotation rate driving force for grain rotation was derived from energy considerations, including the dissipation induced by mass diffusion and that by GB sliding viscosity. The model predicts the effect of softening mechanism for total stress-strain relation; the grain size and mean maximum Schmid factor effect was considered in the phase mixture model. Further discussion was presented for calculation results and relative experimented observations.