Substitutional diffusion was measured in α-Zr monocrystals, and the diffusion profiles were analyzed by using Rutherford back-scattering. The measurements were performed parallel and perpendicular to the specimen c-axis (table 346). The main aim was to study the effect of Fe upon the diffusion of Ta at 1100K. Some preliminary data were also reported for 872 and 1000K. The initial measurements at 1100K showed that the diffusivity decreased in the order: Ta – Hf – Pb. The specimens were then treated so as to

reduce the Fe content (65 to 30ppm[at]) and the diffusion coefficients were re-measured. The diffusion coefficients fell by a factor of about 2 with decreasing Fe concentration. All of the D-values which were found at 1100K lay between 4 x 10-19 and 3 x 10-17m2/s. The results were interpreted in terms of intrinsically normal diffusion, with an enhanced diffusion of the slower diffusing species by an Fe-associated defect. A comparison of solute diffusivity values for α-Zr, where the Fe levels had not been deliberately reduced, showed that substitutional solute diffusion increased with decreasing size and valence.

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 345

Diffusion of Pb in α-Zr