| For steady-state deformation caused by grain-boundary diffusion, the macroscopic creep rate and the effect of viscous grain-boundary sliding in a polycrystal of nano-sized grains are analyzed by the energy-balance method in three dimensions. 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 nano-sized grains are much lower than those predicted by grain-boundary diffusion. |
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