Effect of the Peierls stress on the transition from Harper-Dorn creep to diffusional creep

Abstract

Experimental studies of high-temperature creep at low stresses have shown that polycrystalline materials exhibit a transition from Harper-Dorn (H-D) creep to diffusional creep as the grain size decreases. On the basis of a theoretical analysis, it is predicted that the grain size marking this transition varies inversely with the Peierls stress of the material. It is demonstrated that there is reasonable agreement between this theoretical prediction and experimental observations for a wide range of materials. Therefore it is concluded that, in materials such as oxides, carbides and silicates in which the Peierls stresses are high H-D creep will be dominant over diffusional creep even when the grain size is very small whereas, in materials such as f.c.c. metals and chlorides in which the Peierls stresses are low, diffusional creep will be dominant over H-D creep even when the grain size is very large.