Tracer diffusion of silver in α-zirconium single- and polycrystals

Bulk diffusion of 110mAg was measured in single and polycrystalline α-Zr in the temperature range 895 K - 1117 K. In both cases linear Arrhenius relations were determined with an activation enthalpy Q of (245±10) KJ mol-1 and a preexponential factor D0 of 2.2x10-4 m2 s-1 for α-Zr single-crystals, the diffusion axes of which were tilted 220 from the c-axis of the hcp-lattice. The temperature dependence in the polycrystalline specimens is described by Q=(210±9) kJ mol-1 and D0=6.8x10-6 m2 s-1. In comparison to previously published data all existing bulk diffusion coefficients of Ag in α-Zr single-crystals on the one hand and in α-Zr polycrystals on the other hand are in good agreement, in spite of the different purity of the materials used. Especially no influence of Fe impurities on Ag bulk-diffusion could be detected. The influence of short circuit diffusion paths on the measured diffusion coefficients was carefully examined. Though Ag diffusion turns out to be two to three orders of magnitude faster than Zr self-diffusion at Tα,β, vacancy diffusion seems to be the dominating diffusion mechanism. (orig.)