Rate of creep due to grain-boundary diffusion in polycrystalline solids with grain-size distribution

摘要

For steady-state deformation caused by grain-boundary diffusion, the macroscopic creep rate is analysed for a three-dimensional polycrystal consisting of space-filling grains, by taking into account the effects of diffusional interaction between grains, viscous grain-boundary sliding and grain-size distributions. For regular polyhedral grains, the grain-grain interactions increase the degree of symmetry of diffusional field, resulting in a decrease of the effective diffusion distance. Meanwhile, both the viscous grain-boundary sliding and the grain-size distribution are found to decrease the creep rate. At decreasing grain sizes, the influence of the viscous grain-boundary sliding becomes increasingly important, which explains the recent experimental observations that the creep rates of nanosized grains are much lower than those predicted by grain-boundary diffusion. On the effect of the grain-size distribution, the upper-bound and lower-bound creep rates are estimated.