Manuel J. Iribarren

95Zr Diffusion along the α/β interphase boundaries of a Zr-2.5Nb alloy

Abstract A Zr-2.5Nb alloy was submitted to a heat treatment that resulted in a stabilized two-phase structure, resolvable by optical microscopy and with natural interphase boundaries. Diffusion of 95Zr was studied along the α/β interphase boundaries prepared in the range of temperature 922–1109 K, corresponding to the α+βZr field. The interphase boundary diffusion coefficients obtained were 3 to 4 orders of magnitude higher than bulk diffusion in the corresponding β phase and more than 6 orders with respect to the α phase. The Arrhenius plot shows a straight line that is represented by P i = 1.5 × 10 −4 exp( −306kJ RT ) (m 3 /s) . It is suggested that the results obtained are a suitable approach to extrapolate values of diffusion coefficients at temperatures of interest for nuclear reactors, although the microstructure developed for this research is not the same as that present in pressure tubes in CANDU type reactors.

Ru Self-Diffusion and Ru Diffusion in Al

The self-diffusion of Ru in the temperature range of (1267-1373) K and the Ru diffusion in pure aluminum in the temperature range of (632-873) K is reported. Difficulties were encountered when working with Ru as matrix (its brittleness at room temperature impeded a good sectioning) and they are the reason why only the order of magnitude of the self-diffusion in the small range of temperature studied is given. For Ru diffusion in aluminum, two experimental techniques were used: the conventional serial sectioning with use of a radiotracer, 103Ru, for the highest temperatures and Heavy Ions Rutherford Backscattering Spectrometry (HIRBS) for the lowest ones. The diffusion parameters are: Q = 199.4 kJ/mol and D0 = 4.1x10-2 m2/s. A comparison is made with Ru diffusion behavior in copper and silver.

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.

Grain Boundary Diffusion and Segregation of Co and Cr in Zr-Based Alloys

51Cr and 60Co diffusion along grain boundary (GB) in polycrystalline Zr and -Zr-20%Nb were measured by means of the radiotracer technique in an overall temperature range [380-1000] K. The use of Harrison´s C and B kinetics resulted in direct data of the GB diffusivity (Dgb) and the apparent GB diffusivity (Pgb). The analyzed temperatures involved those of power reactors service. The GB segregation factors s were determined or evaluated in the limit of very dilute solute concentration.