The near threshold behaviour of delayed hydride cracking in Zr-2.5 wt% Nb

摘要

This work studies the behaviour of delayed hydride cracking (DRC) in Zr-2.5 wt% Nb alloy near the threshold stress intensity factor. A modified experimental method was developed, in which specimens are fatigued between consecutive experiments, and a constant load instead of a decreasing load is used in each experiment. The hydride clusters formed and fractured at the crack tip during different experiments are thus separated and studied individually. The plastic deformation on specimen surfaces, the formation and fracture of hydride clusters at the crack tip, and the corresponding acoustic emission (AE) signals were studied, and were found to fall into three categories. It is found that the resistance to DRC increases with increasing crack length due to the plane stress effect on specimen surfaces. The increase in resistance to DHC is associated with an increase in the length of the first few hydride clusters along the crack path. Based on this concept, KIH is more rigorously defined from an experimental perspective.