Effect of the severe plastic deformation temperature on the diffusion properties of the grain boundaries in ultrafine-grained metals

Abstract

A model is proposed to explain the effect of the severe plastic deformation (SPD) temperature on the diffusion properties of the grain boundaries in ultrafine-grained (UFG) metals and alloys. It is shown that an increase in the SPD temperature in UFG metals leads to an increase in the activation energy of grainboundary diffusion from (3–5)k B T m, which corresponds to the diffusion parameters of nonequilibrium grain boundaries, to (8–10)k B T m, which corresponds to the diffusion parameters of equilibrium grain boundaries (k B is the Boltzmann constant, T m is the melting temperature). The dependence of the activation energy of grain-boundary diffusion on the SPD temperature is found to be determined by the kinetics of the competing processes of defect accumulation at grain boundaries and the diffusion accommodation of defects.