Charpy Impact Test of Oxidized and Hydrogenated Zircaloy Using a Thin Strip Specimen

Abstract

The impact properties of an oxidized and a hydrogenated Zircaloy have been studied with an instrumented Charpy machine by using a strip Charpy V-notch specimen (1 mm thick by 4 mm wide). Fracture processes such as crack initiation and propagation were examined using load-displacement curves obtained in this study. In the case of the hydrogenated specimen containing preferentially oriented hydrides, an appreciable decrease in the absorbed energy was observed in the crack propagation rather than in the crack initiation. From results of fractographs of the specimen, it was suggested that the reduction of the crack propagation energy of hydrogenated specimen could be attributed to the change of the stress state in the Zircaloy matrix, which was caused by the fracture of hydride in the inner part of specimen. In the case of the specimen oxidized at 973 K for 60 min, on which an oxide layer (4 μ in thickness) and oxygen incursion layer (4 μm) were formed, the surface layers affected the crack initiation process. The growing oxygen incursion layer, in particular, resulted in the constraint of plastic deformation of the Zircaloy matrix not only in the crack initiation but also in the crack propagation as its thickness increased.

KEYWORDS:

• Zircaloy
• oxide layer
• oxygen incursion layer
• hydride
• Charpy test
• absorbed energy
• crack initiation
• crack propagation