EVIDENCE FOR NABARRO-HERRING CREEP IN METALS - FICTION OR REALITY

It is shown that all creep data in metals ascribed to the Nabarro-Herr ing (N-H) diffusional creep mechanism cannot in fact be definitively d escribed by the N-H creep theory. Rather, the creep mechanism is assoc iated with either Harper-Dorn (H-D) dislocation creep or grain boundar y sliding (GBS). Specific responses are presented to work by Fiala and Langdon (F-L) who have presented opposing views to the above conclusi ons. 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 f or GBS and H-D creep. It is concluded that as long as rigorous and phy sically sound theories for creep controlled by GBS and H-D creep are n ot forthcoming, researchers will continue to use, erroneously in the a uthors' view, the N-H diffusional creep mechanism to explain low stres s creep behavior of polycrystalline solids.