The substitutional diffusion coefficients of Hf, Ta and Pb were measured in α-Zr single crystals, and the diffusion profiles were analysed using Rutherford back-scattering (Hf, Ta, Pb) or secondary ion mass spectrometry (Hf). Measurements were made parallel (D∥) or perpendicular (D⊥) to the specimen c-axis. The main study was concerned with the influence of Fe upon the diffusion of Hf, Ta and Pb at 1100K, but some preliminary data were also reported for Pb and Ta at 872 and 1000K. The initial measurements at 1100K showed that D(Ta) > D(Hf) > D(Pb). The Zr specimens used for these measurements were then treated in order to reduce the Fe content (65-30ppm[at]) and the diffusion coefficients were re-measured. With one exception (D∥ for Hf), the diffusion coefficients fell by a factor of about two with a decrease in Fe concentration and D∥ for Hf fell by about an order of magnitude. All of the D values measured at 1100K for Hf, Ta and Pb lay in the range of 4 x 10-19 to 3 x 10-17m2/s. Those for Hf, and their dependence upon the Fe concentration (with the exception of low-Fe D∥ data), were similar to α-Zr self-diffusion values. The results were considered in terms of intrinsically normal diffusion, with enhancement of the more slowly diffusing species by an Fe-associated defect. A comparison of solute D values, measured in α-Zr where Fe levels had not been deliberately reduced, showed that substitutional solute diffusion increased with decreasing size and valence. Solute Diffusion in α-Zr. Rutherford Backscattering and Secondary-Ion Mass Spectrometry Study. G.M.Hood, T.Laursen, J.A.Jackman, R.Belec, R.J.Schultz, J.L.Whitton: Philosophical Magazine A, 1991, 63[5], 937-47

Table 94

Diffusion of Hf in Polycrystalline Ultra-Pure or Fe-Doped -Zr