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    STP1023

    Diffusion of 3D Transition Elements in α-Zr and Zirconium Alloys

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    Abstract

    Measurements of tracer diffusion coefficients D of Fe-59, Ni-63 and Cr-51, in zirconium single crystals and of Fe-59 in some zirconium alloys have been made. The single crystal measurements were made in directions both parallel Dǁ and perpendicular D to the c axis of the specimens; results for nickel were obtained at 1025, 883, and 674 K and for iron at 674 K. The low temperature diffusion profiles are generally complex and indicate the probable operation of more than one diffusion process. The diffusion behavior of nickel in zirconium seems to parallel that of iron, for which more data are available and, probably, that of cobalt; at high temperatures, the effective activation energy for diffusion hD is approximately 0.6 eV, while at lower temperatures, a value closer to 2.0 eV seems more appropriate. The diffusion profiles indicate that Dǁ D at all temperatures, though there is a tendency for the anisotropy to diminish as the temperature decreases. The high-temperature results, associated with intrinsic behavior, conform to previously developed, diffusion parameter/atomsize correlations. The lower temperature data are probably symptomatic of complexing and precipitation effects. Chromium diffusion measurements have been made at 887, 977, and 1114 K. The diffusion profiles are generally well-behaved, and D(T) obeys the customary Arrhenius law D = D° exp (-hD/kT) with values of 2.4 × 10-6 2and 9.5 × 10-6 m2s for D°(ǁ) and D°(⊥), respectively, and 1.39 and 1.61 eV for the corresponding hand h°⊥ parameters. The chromium D values are in general agreement with some earlier data; Dǁ is from 2.6 to 5.2 D, and the ratio increases with decreasing temperature.

    In addition to the above, measurements of iron diffusion in Zircaloy-2 and Zr-2.5wt% Nb have been made at 893 and 1122 K. The diffusion profiles are reasonably well behaved; the associated Ds are from 20 to 100 times lower than corresponding D(Fe) values for nominally pure single crystal α-Zr; the alloy D(Fe) results are very similar to previous, corresponding D(Ni) data for these alloys. Isolated diffusion measurements have also been made on a Zr-1.08 at% Sn alloy, at 1121 K, and on single crystals of Zr-0.1 at% Fe, at 1054 K. The values of Dǁ|, D, and the associated ratio, Dǁ/D, for the Zr(Fe) alloy are all somewhat lower than the corresponding data for iron diffusion in pure α-Zr. In addition, the Zr(Fe) alloy showed remarkable compositional variations; some comment on this behavior is made.

    Keywords:

    Alpha-zirconium, single crystals, zirconium alloys, 3D transition elements, tracer diffusion, activation energies, anisotropy, size-effect correlation, microscopy, compositional variations


    Author Information:

    Hood, GM
    Research scientist and research technologist, Chalk River Nuclear Laboratories, Chalk River, Ontario

    Schultz, RJ
    Research scientist and research technologist, Chalk River Nuclear Laboratories, Chalk River, Ontario


    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP18880S