DIFFUSION-CONTROLLED DISLOCATION CREEP - DEFENSE

A defense is made to the criticisms of Poirier against diffusion-controlled dislocation creep. The criticism that values of the activation volumes of creep offer no strong support to diffusion-controlled dislocation creep is turned around and is shown to be strong evidence against non-diffusion-controlled dislocation creep. It is shown that, just as in very fine grain material Coble creep takes over from Nabarro-Herring creep as the temperature is lowered, pipe diffusion will take over from bulk diffusion as the process-controlling dislocation climb. Thus the existence of low values of the creep activation energy in the low temperature range of high temperature creep is readily explained. It is shown that dislocation glide processes cannot account for these low activation energies unless one is willing to accept that for 21 metals it is only a remarkable coincidence that at relatively high temperatures the activation energy of creep is equal to the activation energy for self-diffusion. © 1979.