STP1132: Corrosion-Electrochemical Properties of Zirconium Intermetallics

    Weidinger, HG
    Siemens KWU AG, Erlangen,

    Ruhmann, H
    Siemens KWU AG, Erlangen,

    Cheliotis, G
    Siemens KWU AG, Erlangen,

    Maguire, M
    Teledyne Wah Chang, Albany, OR

    Atomic Energy of Canada Ltd., Chalk River, Ontario

    Yau, T-L
    Teledyne Wah Chang, Albany, OR

    Pages: 37    Published: Jan 1991


    Abstract

    Alpha-zirconium is a very poor solvent for most alloying metals. Moreover, it has a high affinity for these metals. Consequently, intermetallics are easily formed and highly visible in zirconium and its alloys. Many researchers believe that the corrosion resistance of zirconium and its alloys depends strongly on the distribution and morphology of these intermetallics. Corrosion problems, such as nodular corrosion and intergranular corrosion, are often associated with intermetallics.

    Numerous papers have been published concerning the role of intermetallics in nodular corrosion of Zircaloys. Several mechanisms have been proposed for nodule initiation and growth. They include one or more of the following factors: local solute depletion, electrochemical effects, oxide ductility, electronic and ionic conductivities of the surface oxide, induced stresses, and oxide structure transformation.

    However, very limited studies have been directly done on the corrosion properties of these intermetallics. Therefore six intermetallics (Zr2Fe, Zr3Fe4Cr2, Zr10Fe3Ni2, Zr4Sn, ZrCr2, and 3Zr2Ni) were prepared for corrosion and electrochemical tests. These intermetallics were chosen since tin, iron, chromium, and nickel are the principal alloying elements in Zircaloys, and the selected intermetallics have been identified in the alloy matrix. In addition to these intermetallics, Zircaloy-2, Zircaloy-4, and crystal-bar zirconium were also included in this study.

    Corrosion and electrochemical tests on selected materials at both ambient and elevated temperatures were performed at Teledyne Wah Chang Albany and at Siemens AG-KWU Group. Selected materials were characterized using SEM/EDX examinations, potential measurements and autoclave tests. From this information the role(s) of intermetallics on corrosion resistance in water and steam are discussed. A new electrochemical-mechanical-passivity (EMP) model is offered to explain observed oxidation of Zircaloy-2 and Zircaloy-4.

    Keywords:

    Zircaloy, electrochemical properties, intermetallics, second phase, nodular corrosion, BWR, PWR, oxidation, oxidation model, rest potential, open circuit potential, galvanic coupling, steam autoclave testing, oxide films


    Paper ID: STP25525S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP25525S


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