Effect of dispersion and spheroidization treatment of delta zirconium hydrides on the mechanical properties of Zircaloy

This study is basic research on some mechanical properties of Zircaloy-4 and Zircaloy-2 addressed particularly to the influence of hydrogen attack and of the hydride-orientation and -shape effect. At room temperature, Zircaloy-4 has almost the same tensile properties as does Zircaloy-2, both before and after hydriding. Zircaloy-4 may serve well if its hydrogen content is lower than 300 ppm, although hydrogen embrittlement can be alleviated by elevated temperature. If we performed a spheroidization treatment on the platelet hydrogen in the matrix, it may serve satisfactorily when the hydrogen content is 650 ppm or more. Tensile tests of annealed Zircaloy-2 specimens, of hydrided specimens, and of spheroidized specimens containing two different hydrogen concentrations were carried out at temperatures up to 7000C. The strain-rate effect on the mechanical properties was also studied for Zircaloy-2 specimens. The results show that a spheroidization treatment of the hydrided Zircaloy-2 can improve its mechanical properties - i.e., its ductility, toughness, and strength - as well as its hardenability