RAPID-PAIR-ENHANCED DIFFUSION IN ALPHA-ZR AND ITS INTEGRATION INTO THE POINT-DEFECT SCENARIO IN HCP METALS

After a brief review of our present knowledge on intrinsic point defects in h.c.p. metals, an interpretation of self-diffusion and foreign-atom diffusion in both the bulk and the grain boundaries of alpha-Zr is presented. It is demonstrated that rapidly diffusing foreign-atom-vacancy pairs play an outstanding role. In particular, Fe-atom-vacancy pairs control not only the bulk and grain-boundary diffusion of Fe but also the bulk self-diffusion in alpha-Zr. Atomistic models of the configurations, the formation and the diffusion of rapid foreign-atom-vacancy pairs are proposed. Finally, it is concluded that, on the one hand, alpha-Zr shows the anomaly of rapid-pair-enhanced diffusion whereas, on the other hand, isolated monovacancies in alpha-Zr behave normally. For instance, they undergo long-range migration in the recovery stage IV (450-550 K) in accordance with the so-called two-interstitial model.