EFFECT OF OXIDATION ON HERRING-NABARRO CREEP IN MAGNESIUM

Recent observations of dislocation climb in thin electron microscope foils annealed in an oxidising environment have shown that a growing oxide film can act as a source of vacancies. The vacancies produced during oxidation have important consequences on the high temperature mechanical properties of the metal and in particular on Herring-Nabarro creep. The rate of steady-state diffusion controlled creep of zinc and magnesium specimens has been measured as a function of the annealing environment and it has been shown that for fine grained magnesium specimens the rate of creep is greater in an inert atmosphere than in an oxidising atmosphere. These results are in accord with the vacancy concentration gradients produced by oxidation opposing those set up by the applied stress system. No change in creep rate was detected in the zinc specimens which had a large grain size and the injected vacancies clustered to form voids near the oxidising surface. © 1969.