Examination of the plastic properties of Zircaloy-4 at elevated temperatures in air atmosphere

Results are reported about the examination of the influence of test temperatures and sample anisotropy upon the yield stress, the strain rate sensitivity and the ductility of Zry-4 sheet-type tensile specimens. Most of the investigations were performed in air atmosphere in the temperature range between 750 and 1050degC at cross-head speeds ranging over three orders of magnitude. Superplastic deformation behaviour was observed at temperatures between 860 and 1000degC for a strain rate of the order of 10-4s-1. For samples deformed under these conditions in air atmosphere the strain rate sensitivity index msub(a) has shown to depend sensitively upon strain. Although no influence of anisotropy upon the yield stress was observed above 550degC, in the superplastic region msub(a) revealed a strong dependence upon sample orientation. For higher temperatures even in air the total elongation increased with temperature up to 850degC. At the highest temperature due to severe take-up of oxygen the samples failed brittle. The apparent activation energy for superplastic flow agrees very well with the energy of grain boundary diffusion in α-Zr. (Auth.)