Diffusion along grain and interphase boundaries in alpha Zr and Zr-2.5 wt pct Nb alloy

Diffusion parameters of Cr diffusion along the α/β interphase boundaries of a Zr-2.5 wt pct Nb alloy are presented. The conventional radiotracer technique combined with serial sectioning of the samples was applied. In the Arrhenius plot, it is possible to consider only one straight line (with Q=133 kJ/mol for 615<T<953 K) or two zones (with Q=230 kJ/mol for 773<T<953 K and Q=77 kJ/mol for 615<T<773 K). An analysis is made of these results together with previous data concerning diffusion along short circuits paths in α-Zr (grain boundaries) and Zr-2.5 wt pct Nb (interphase boundaries): Zr and Nb as the alloy component elements and Ni, Fe, and Co as other relevant impurities. Different mechanisms are proposed: a vacancy mechanism for Zr and Nb and an interstitial-like mechanism for the impurities, for both kind of boundaries. The influence on diffusion and the estimated values of the impurities segregation in the α phase are discussed in the work. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.