Hydride-induced degradation of hoop ductility in textured zirconium-alloy tubes: A theoretical analysis

Hydride-induced degradation of hoop ductility in Zr-alloy tubular components has been studied for many years because of its importance in the nuclear industry. In this paper the role of intergranular and intragranular δ-hydrides in the degradation of ductility of the textured Zr-alloy tubes is investigated. The correlation among hydride distribution, orientation and morphology in the tubes is formulated based on thermodynamic modeling, and then analyzed. The results show that the applied stress, the crystallographic texture of α-Zr matrix, the grain-boundary structure, and the morphology and size of Zr grains simultaneously govern the site preference and the orientation of hydrides. A criterion is proposed to determine the threshold stress of hydride reorientation. The hoop ductility of the hydrided Zr tubes is discussed using the concept of macroscopic fracture strain. It is shown that the intergranular hydrides may be more deleterious to ductility than the intragranular ones. This work defines a general framework for understanding the relation of the microstructure of hydride-forming materials to embrittlement.