Self-diffusion was studied in -phase monocrystals, which contained about 50ppm of Fe, at temperatures of between 867 and 1107K. The diffusivity was measured in directions which were parallel or perpendicular to the c-axis. Measurements were also performed on -phase monocrystals, which contained less than 1ppm of Fe, at 1110K. The diffusivities were determined by using a 95Zr tracer, and serial sectioning techniques. The latter involved sputtering or microtoming. It was found that the diffusivities in the lower-purity material were an order of magnitude higher than those in the higher-purity material. The anisotropy of the diffusivity exhibited a complicated behavior. Thus, the parallel/perpendicular ratio of sputter-sectioned low-purity material increased from 1.0 to 3.2 with decreasing temperature. On the other hand, the ratio had a constant value of 0.53 in both microtomed low-purity material and sputter-sectioned high-purity material. The low ratio was consistent with intrinsic self-diffusion in hexagonal close-packed metals with c/a ratios of less than 1.633.

G.M.Hood, H.Zou, D.Gupta, R.J.Schultz: Journal of Nuclear Materials, 1995, 223[2], 122-5