Effect of the circumferential hydrides on the deformation and fracture of Zircaloy cladding tubes

The hydride formation and its effect on the deformation and fracture of two different types of Zircaloy cladding tubes were investigated. The effect of cooling rate on the size and distribution of hydrides were also examined. Hydrides were more homogeneously distributed with high cooling rate (i.e., air-cooled) and clustered with low cooling rate (i.e., furnace-cooled). The room temperature strength increased slightly and the ductility decreased with the formation of the hydrides. The mechanical properties were slightly modified by the size and distribution of hydrides. Secondary cracks along the platelets of hydrides were observed on the fracture surfaces of tubes. The slight loss of ductility in the presence of circumferential hydrides is thought to be associated with the secondary cracking during the final process of the fracture. The deformation behavior of the tubes was not greatly influenced by the presence of the circumferential hydrides. The rate controlling mechanism of the deformation can be explained by the dislocation intersection mechanism in which the segregation of alloying elements on dislocations affects the activation length.