A comparative study of hydride-induced embrittlement of Zircaloy-4 fuel cladding tubes in the longitudinal and hoop directions

In this work, the mechanical behavior of as-received and hydrogenated Zircaloy-4 fuel claddings was investigated by the newly developed advanced expansion due to compression (A-EDC) test and the conventional uniaxial tension (UT) test at room temperature, in order to, respectively, understand the hydride-induced embrittlement in tube longitudinal and hoop directions. The UT experimental results showed that the mechanical strength in the longitudinal direction slightly increased with hydrogen content, whereas the maximum strain decreased greatly with hydrogen increasing. In the case of A-EDC tests, the mechanical performance in the hoop direction seemed insensitive to the hydrogen content; no obvious decline in maximum strain was observed until 800 ppm H. The comparison between these two tests clearly reveals that the hydride-induced embrittlement is preferential to occur in the longitudinal direction, compared with the sluggish response in the hoop direction, which implied the enhanced ductility anisotropy due to hydrides. In the post-tests observation, the fracture morphologies became gradually distinct for the as-received and hydrided samples examined by UT and A-EDC methods, and different orientation relationships between the applied stresses and hydrides distribution would be responsible for that distinction.