COMPARISON BETWEEN INTERPHASE-BOUNDARY AND GRAIN-BOUNDARY DIFFUSION IN ZIRCONIUM-BASED MATERIALS

Grain-boundary diffusion (GBD) measurements made in alpha-Zr have been compared with interphase-boundary diffusion (IBD) made in the two-phase field alpha + beta-Zr of Zr-2.5% Nb, with the aim of gaining a better understanding of the behaviour of these boundaries in Zr-based materials, which are relevant for the nuclear industry. In addition to the substitutional diffusing elements Zr and Nb, the theoretically interesting and technologically important case of fast-diffusing bulk interstitials such as Fe, Co and Ni was investigated in GBD and IBD. The results obtained have been considered in a comprehensive comparison. The fastest mobility was found for GBD of Fe in alpha-Zr and the slowest for Zr GBD in alpha-Zr. Both sets of data differ by roughly eight orders of magnitude. The results obtained suggest that diffusion takes place by different mechanisms: vacancies for the substitutional elements Zr and Nb and some type of interstitial mechanism for Fe, Co and Ni. When comparing the total sets of data of GBD and IBD, it turns out that, from the diffusion point of view, both types of boundary provide similar short-circuit diffusion paths.