Effect of hydride precipitation on the fatigue cracking behavior in a zirconium alloy cladding tube

Abstract

Zirconium (Zr) alloys, which are widely used as the fuel cladding tubes in the nuclear industry, suffer from the hydrogen embrittlement issues resulting from the precipitation of brittle hydrides. The fatigue crack initiation and propagation behavior at room temperature in a Zr-Sn-Nb-Fe alloy tube material containing the hydrides of the axial and hoop orientations are investigated. The results show that the fatigue cracking initiates at the hydrides. The sensitivity of hydride-induced cracking is largely dependent on the hydride orientation with respect to the applied stress direction. When the hydride platelets are oriented with their longitudinal direction perpendicular to the applied stress, the hydrides facilitate the development of fatigue cracking in the tube material. A micromechanical stress analysis qualitatively describes the stress state of the hydrides subjected to the fatigue loading. The analysis shows that the hydrides tend to crack along the direction perpendicular to the maximum principal stress. The fatigue crack propagation under cyclic shear stress is found to be facilitated along the Zr matrix–hydrides interface, in contrast to the ductile Zr matrix which may blunt the development of crack tips. Further fatigue crack nucleation and propagation proceeds along the slip bands in the Zr matrix at significant fatigue loading cycles, leading to the eventual fatigue failure of the investigated cladding tubes with a relatively low hydrogen content (~260 ppm).