Hydride-induced degradation of zirconium alloys: a criterion for complete ductile-to-brittle transition and its dependence on microstructure

Hydride-induced embrittlement is an important problem in hydride-forming materials. In this paper, a model is built for analysing a hydride-induced degradation process of the mechanical properties of zirconium alloys. A time-dependent criterion is proposed for determining the critical conditions of complete ductile-to-brittle transition. The dependence of this criterion on microstructure of Zr alloys is analysed in detail. The results show that many factors simultaneously govern the hydride-induced degradation. These factors include the susceptibility of hydrides to rupture, hydride size, hydride distribution, active slip systems, zirconium grain orientation, grain-boundary structure, grain-boundary density, hydrogen concentration, applied stress state and temperature. Intergranular hydrides have a more important influence on the loss in ductility than intragranular ones. The results obtained in this paper are of particular interest for zirconium alloys used in nuclear application.