Abstract
An oxygen-enriched Zircaloy-2 alloy (4180 ppm 0) and an industrial grade of Zr-2.5Nb were hot compressed in the temperature range 750–1000°C at constant true-strain rates in the range 10−4 to 10−1 S−1. Significant yield drops were detected in the Zircaloy-2 followed by normal work hardening. The magnitude of the yield drop increased with temperature and therefore with β-phase fraction, and a strong but slow strain-aging response was observed at 1000°C. By contrast, the Zr-2.5Nb alloy displayed flow softening in the (α+β)-phase field, changing to normal flow in the single-phase β region. The amount of flow softening decreased with an increase in the β-phase fraction and is ascribed to the coarsening of the fine Widmanstätten or martensitic structure produced by the prior heat treatment, leading to an equiaxed structure at large strains. The comparatively weak strain-aging effect and the relatively fast aging kinetics in the Zr-2.5Nb alloy suggest the involvement of Nb-rich clusters in this material. The contrasting aging behaviour of the oxygen-enriched Zircaloy-2 indicated that ordered zones of the β-stabilizing elements Fe and Cr are responsible in the latter case.
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