Migration assisted diffusional creep by grain-boundary diffusion

Diffusional creep by interface diffusion in multicomponent systems with stationary interfaces is controlled by the slowest diffusing species along its fastest path. The concentration gradients along the interfaces are always biased against the faster diffusing species and tend to eliminate any differences in diffusional fluxes of various species due to different mobilities. These gradients are reduced drastically when the interface migrates and leaves in its wake an alloyed or de-alloyed zone. Diffusional creep in this case is controlled by the fastest diffusing species and is significantly faster. The transition to migration assisted diffusional creep may give rise to a threshold behavior corresponding to the on-set of migration. It is possible for diffusional creep of this type with attendant boundary migration to achieve large strains by maintaining an equiaxed grain shape, a feature characteristic of superplasticity. The effect is also closely related to several other observations in ceramics and geology