ALPHA-ZR SELF-DIFFUSION ANISOTROPY

Self-diffusion coefficients (D) have been measured in nominally pure ( NP) alpha-Zr single crystals (approximate to 50 ppm Fe) in the range 8 67-1107 K, in directions either parallel (D-pa) or perpendicular (D-pe ) to the c-axis. Measurements were also made on high-purity (HP) alpha -Zr single crystals(< 1.0 ppm Fe) at 1110 K. The diffusion profiles we re determined by sectioning and radio-tracer (Zr-95) counting. Section ing was done with a sputtering device, or a microtome (some NP experim ents at 1107 K). D values for NP Zr are about an order of magnitude hi gher than the corresponding values for HP Zr. Diffusion anisotropy is complicated. The sputter-sectioned NP Zr specimens show increasing ani sotropy ratios (AR = D-pa/D-pe), from 1.0 to 3.2, with decreasing temp eratures, whereas AR approximate to 0.53 for both the microtome-sectio ned NP and sputter-sectioned HP Zr: the low AR value is consistent wit h expectations based on intrinsic self-diffusion in hcp metals with c/ a < 1.633.