Evidence for Nabarro-Herring creep in metals: fiction or reality?

Abstract

It is shown that all creep data in metals ascribed to the Nabarro-Herring (N-H) diffusional creep mechanism cannot in fact be definitively described by the N-H creep theory. Rather, the creep mechanism is associated with either Harper-Dorn (H-D) dislocation creep or grain boundary sliding (GBS). Specific responses are presented to work by Fiala and Langdon (F-L) who have presented opposing views to the above conclusions. Creep data for copper used by F-L to support N-H creep are shown to be incompatible with the theory, since the experimental creep rates are about three orders of magnitude higher than predicted. The copper creep data, however, can be predicted by phenomenological equations for GBS and H-D creep. It is concluded that as long as rigorous and physically sound theories for creep controlled by GBS and H-D creep are not forthcoming, researchers will continue to use, erroneously in the authors' view, the N-H diffusional creep mechanism to explain low stress creep behavior of polycrustalline solids.