THE ANISOTROPY OF HF DIFFUSION IN ALPHA-ZR

Hf diffusion coefficients (D) have been measured (similar to 870-1100 K) in directions parallel (D-pa) and perpendicular (D-pe) to the c-axi s of double-faced, single-crystal specimens of both high purity (HP) a nd nominally pure (NP) alpha-Zr. The diffusion profiles were measured by secondary ion mass spectrometry. Hf diffusion in HP alpha-Zr is cha racterised by an activation energy of about 3.0 eV and a pre-exponenti al factor of about 10(-5) m(2)/s. The anisotropy ratio, D-pa/D-pe, is similar to < 1.0 for the HP specimens and mostly > 1.0 for the NP spec imens. A dependence of D on diffusion time/depth is indicated for some experiments on NP Zr.