Failure of Hydrided Zircaloy-4 Under Equal-Biaxial and Plane-Strain Tensile Deformation

The fracture behavior of unirradiated Zircaloy-4 containing either solid hydride blisters or hydrided rims has been examined for the contrasting conditions of equal-biaxial and plane-strain tensile deformation at three temperatures (25°, 300°, and 375°C). Cold-worked and stress-relieved Zircaloy-4 sheet containing hydride blisters shows nearly identical failure strains in equal-biaxial and plane-strain tensile deformation for a wide range of blister or rim depths. In all cases, failure strains decrease rapidly with increasing hydride blister or rim thickness, especially in the ≤100 µm range. Test temperature has a significant effect on ductility with failure strains at 300° and 375°C being much greater than at room temperature. The results indicate that the ductility of material containing hydride rims/blisters greater than ≈ 30–40 µm deep is limited by crack growth, which occurs in a mode I manner at 25°C but in a mixed mode I/II manner at ≥300°C (and at higher failure strain levels).