The origin of anisotropy DHC behavior in Zr-2.5%Nb pressure tube materials

In order to explain the anisotropy of delayed hydride cracking (DHC) behavior in the longitudinal and in radial direction in Zr-2.5%Nb pressure tube materials, DHC tests using compact tension (CT) and cantilever beam (CB) specimens and tensile tests using small specimens with a gage length of about 2 mm have been carried out, and the texture change in the DHC surfaces have been examined. It has been found that the deformation mechanisms operating during the cracking process were significantly different in both specimens. The (10-12) twinning system operated when a DHC crack propagated in the longitudinal direction and both the (11-1) and (10-2) twinning systems operated when the DHC crack propagated in the radial direction. The tensile results showed that there is anisotropy of the tensile behavior and the strength in the radial direction is minimum in the range of 100-400oC. This behavior seems to be due to the anisotropy of texture. Therefore, it can be concluded that the differences in crack propagation behavior between CT and CB specimens is due to the differences in deformation mechanisms which are resulted from the anisotropy of the texture. (author)