Effects of Irradiation and Hydriding on the Mechanical Properties of Zircaloy-4 at High Fluence

Abstract

Tension and burst tests were conducted on irradiated Zircaloy-4 charged with hydrogen. The investigated ranges of experimental variables were deformation temperatures, 298 to 673 K; fluence levels, 7 to 12 × 1021 n/cm2, E > 0.821 MeV; and hydrogen concentrations, 50 to 400 ppm. The data show a significant reduction in the elongation compared to the properties of Zircaloy-4 with lower levels of fluence and hydrogen concentration. Although the overall elongations of the specimens were low, the fracture surface examination showed evidence of ductility in the material and localized deformation bands were observed on the specimens deformed at higher temperatures. The inhomogeneous deformation bands, observed predominantly for deformation temperatures between 573 to 673 K, are consistent with the literature evidence of dislocation channeling in highly irradiated Zircaloy. Radiation anneal hardening was observed at the temperature interval of 573 to 623 K. Since the orientations of both the habit plane of hydrides in Zircaloy and the dislocation channels formed during deformation at ȼ600 K are close to the basal plane, hydrides appear to initiate fracture in the dislocation channels in highly irradiated Zircaloy containing quantities of hydrogen above the solubility limit. A failure mechanism involving hydride initiated fracture in dislocation channels is suggested for irradiated Zircaloy deformed at ȼ600 K. Mechanical property data on irradiated Zircaloy in recent literature appear to be consistent with the proposed failure mechanism. An alloy development program is suggested to enhance the ductility of highly irradiated Zircaloys.