Nb 95 and Ni 63 diffusion along the α¦β interphase boundaries of A Zr-2.5 wt% Nb alloy

Abstract

The diffusion of Nb 95 and Ni 63 has been studied in a Zr-2.5 wt% Nb alloy. The specimens were prepared by means of heat treatments that provided a stabilized two-phase structure, resolvable by optical microscopy, and with natural interphase boundaries. Diffusion of Nb 95 was studied in the 702–818°C temperature range, corresponding to the α + β field. The interphase boundary diffusion coefficients obtained in this work were 3 to 4 orders of magnitude higher than the bulk Nb diffusion coefficient in pure Zr. The Arrhenius plot appeared not quite linear. The activation energy varied from 105 kJ/mol for low temperatures to 230 kJ/mol for high temperatures. Diffusion of Ni 63 was studied at 801 °C by means of autoradiographs. X-ray and stripping film autoradiographs were obtained at several depths, showing at small depths a non uniform tracer distribution, in coincidence with the distribution of both phases. At greater depths the network of interphase boundaries is observed as darker lines.