STP1423: Role of the Second-Phase Particles in Zirconium Binary Alloys

    Barberis, P
    CEZUS Research Center, Ugine,

    Ahlberg, E
    Göteborg University, Göteborg,

    Simic, N
    Göteborg University, Göteborg,

    Charquet, D
    CEZUS Research Center, Ugine,

    Lemaignan, C
    CEA Grenoble, Grenoble,

    Wikmark, G
    Advanced Nuclear Technology, Uppsala,

    Dahlbäck, M
    Westinghouse Atom AB, Västerås,

    Limbäck, M
    Westinghouse Atom AB, Västerås,

    Tägtström, P
    Westinghouse Atom AB, Västerås,

    Lehtinen, B
    BL Electron Microscopy, Haninge,

    Pages: 26    Published: Jan 2002


    Abstract

    The second-phase particles (SPP) play an important role on the corrosion and hydriding properties of BWR Zircaloy-type materials. It has been proposed that the chemical composition of the SPPs as well as the SPP size distribution strongly affect the in-reactor performance. Zr-Fe, Zr-Cr, and Zr-Ni binary alloys were processed, the size and density of SPP being independently varied through chemical composition and heat treatments.

    SEM imaging was used to measure the grain size and the SPP size and distribution. Significant differences between binary alloys with iron, chromium, and nickel were observed. Grain sizes depend primarily on size and volume fraction (VF) of SPP. The SPP kinetic growth varies with the alloying element.

    These observations are compared with corrosion and hydriding data obtained from autoclave experiments at 415 and 500°C, which show that besides the SPP size, their volume fraction is an important parameter (increasing the volume fraction decreases the corrosion rate, whatever the nature of the SPP). On the contrary, air oxidation at 415°C shows very slight influence of SPP type, size, and volume fraction on the corrosion resistance of the material. It should, however, be noticed that the considered test was a short-term test (3 days) and that the oxide layer thickness was less than or around 1 μm for all tested materials.

    Electrochemical impedance spectroscopy as well as potential sweep and step experiments were used to study the oxidation properties of the binary alloys at room temperature. On samples with large particles, thin compact oxide films are formed. In contrast, on samples with many small particles thick porous oxides are formed.

    Based on these results and the SPP volume fraction, a tentative mechanism of corrosion and hydriding is proposed, explaining the differences in uniform and nodular corrosion observed between different Zr-based alloys.

    Keywords:

    zirconium alloys, corrosion, precipitate, intermetallic compound, electrochemistry, grain size


    Paper ID: STP11382S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP11382S


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