STP681: Predicting High-Temperature Transient Deformation from Microstructural Models

    Sills, HE
    Mathematician and metallurgist, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario

    Holt, RA
    Mathematician and metallurgist, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario

    Pages: 17    Published: Jan 1979


    Abstract

    We have developed a multicomponent model to describe the transient plastic deformation of Zircaloy fuel sheathing during postulated loss-of-coolant accidents (LOCA). From deformation maps, we identify three creep mechanisms, which in principle, occur in all three phase fields of Zircaloy-4 (α, α + β, β): diffusional creep, dislocation creep and athermal strain. Diffusional creep (phase boundary or grain boundary sliding) is modeled in the α and α + β phase fields. Dislocation creep is modeled in all three phase fields and controlled by a work-hardening/recovery expression. Athermal strain has practical significance only at lower temperatures (< 900 K). The sum of the strain rates of the three deformation mechanisms is the total plastic strain rate. At a particular point in the stress-temperature field, one mechanism usually dominates.

    Microstructural changes that affect deformation are also taken into account; these are changes in grain structure, recrystallization, and the α ⇌ (α + β ) ⇌ β phase transformation. When two components are present (α + β or recrystallized and unrecrystallized), they are assumed to deform with equal rates according to the appropriate single-phase model.

    The individual components of the model give excellent agreement with the isothermal data on which they are based, and the entire model gives very good agreement with transient data over a range of temperatures from 700 to 1600 K, a range of heating rates from 0 to 100 K/s, and a range of strain rates from 10-5 to 10-1 s-1. Several applications of the model in evaluating the history dependence of deformation are given.

    Keywords:

    zirconium, nuclear reactors, high-temperature deformation, microstructure, modeling, loss-of-coolant accident


    Paper ID: STP36688S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP36688S


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