STP754

    Flow Stress of Oxygen-Enriched Zircaloy-2 Between 1023 and 1873 K

    Published: Jan 1982


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    Abstract

    The solute strengthening effect of oxygen in commercial-purity Zircaloy-2 was investigated over the temperature range 1023 to 1873 K, strain rate range 10−4 to 10−1s−1, and oxygen concentration range 1260 to 12 360 ppm. The flow parameters were determined in the fully α and fully β as well as (α + β) phase domains. In the two-phase region, the flow curves were characterized by significant yield drops as long as the β volume fraction was over about 50 percent. This effect is ascribed to the enrichment of the β-phase in the substitutional solutes iron and possibly chromium. The flow curves were otherwise normal. For the single-phase α and β structures, the yield and steady-state stresses obeyed the general relation σ = σ0 exp (kc), where σ0 and k are constants, and c represents the oxygen concentration (weight percent). The average values of kα and kβ were determined to be 0.57 ± 0.06 and 0.34 ± 0.10, respectively. The strain rate sensitivities fell in the following ranges, depending on the phases present: 0.15 to 0.20, 0.27 to 0.32, and 0.22 to 0.25 for the α, β, and (α + β) materials, respectively. The experimental activation energies decreased with stress in the ranges 450 to 330 kJ/mol (50 to 150 MPa) and 150 to 120 kJ/mol (1 to 5 MPa) for the α- and β-Zircaloy-2, respectively. The extrapolated zero stress values of Q were 530 and 170 kJ/mol, and are associated with the dominant dynamic recovery mechanism in each phase. The observed steady-state as well as yield stresses correspond closely to the rule-of-mixtures predictions but lie considerably above the values interpolated from the fully α-phase and fully β-phase. This is ascribed to the very powerful strengthening effect of oxygen on the α-phase when it is enriched during the formation of two phases from either single-phase region.

    Keywords:

    nuclear industry, zirconium, Zircaloy-2, fuel sheathing, flow stress, yield drops, steady-state stress, dynamic recovery, flow activation energy, pseudobinary Zircaloy-0 phase diagram, oxygen enrichment, rule of mixtures, oxygen sensitivity, solute strengthening, strain rate sensitivity


    Author Information:

    Choubey, R
    Professor of mechanical metallurgy and graduate student, McGill University, Montreal, Que.

    Jonas, JJ
    Professor of mechanical metallurgy and graduate student, McGill University, Montreal, Que.

    Holt, RA
    Scientists, Fuels and Materials Division, Atomic Energy of Canada Ltd., Chalk River, Ont.

    Ells, CE
    Scientists, Fuels and Materials Division, Atomic Energy of Canada Ltd., Chalk River, Ont.


    Paper ID: STP37062S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP37062S


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