On the transition from power-law creep to diffusional creep

Experimental studies of high-temperature creep have shown that polycrystalline materials exhibit a transition from power-law creep to diffusional creep as the applied stress decreases. On the basis of a theoretical analysis, it is predicted that the stress marking this transition varies not only with the grain size and the stress exponent n for power-law creep, as concluded before, but also with the Peierls stress tau(p) of the material if n > 3 such that, the higher tau(p), the higher is sigma(t), under otherwise identical conditions. It is demonstrated that there is a reasonable agreement between this theoretical prediction and experimental observations for a wide range of materials.