Effects of microstructural inhomogeneity on dynamic grain growth during large-strain grain boundary diffusion-assisted plastic deformation

Abstract

Mesoscale simulations of grain-boundary (GB) diffusion creep in which GB migration-induced static grain growth is suppressed were carried out based on the variational principle of dissipated power. Assuming that the boundaries exhibit no sliding resistance in response to shear stress, the variation of the normal-stress distribution and the diffusive fluxes along the grain boundaries during Coble creep were analysed. The effects of microstructural inhomogeneity, including topological and physical inhomogeneity (i.e. distributions in the grain sizes and GB diffusivities) were investigated. We find that because of the lack of GB migration as an accommodation process to relax the stress concentrations in the microstructure, a topologically inhomogeneous microstructure becomes unphysical at high strains (of typically between 50–100%). Consistent with earlier simulations by Pan and Cocks (1993 Comput. Mater. Sci. 1 95), we find that even in the absence of static grain growth an inhomogeneous microstructure exhibits dynamic grain growth induced by grain-switching induced grain-disappearance events. Our simulations also reveal that in a topologically inhomogeneous microstructure, the diffusive fluxes along any given GB can be in the same direction at both delimiting triple points; i.e. qualitatively different from a homogeneous (i.e. regular hexagonal) microstructure in which, according to Spingarn and Nix (1978 Acta Metall. 26 1389), these fluxes oppose each other.