Synchrotron X-ray diffraction study of zirconium hydride distribution in Zr-2.5%Nb and its redistribution during thermal cycling

Hydride distribution in a dual-phase hydrided Zr-2.5wt%Nb has been studied. Samples having different prior thermo-mechanical processing history were thermally cycled within a 86 keV X-ray photon beam. The diffraction patterns generated with this technique allow the evaluation of the relative quantity of hydrides within differently oriented grain sets. It was found that hydrides exist primarily within two different alpha-Zr grain-sets. One grain-set has its {0002} alpha-Zr direction oriented very close to the hoop direction while the other exists within a plane approximately 20 degrees away from it. During thermal cycling, the proportion or hydrides oriented within different grain sets was shown to change from the distribution associated with the prior thermomechanical processing, to that corresponding to the current thermal cycling conditions. It was also shown that the ability for hydrogen to redistribute in the matrix correlates with the cooling rate of the specimen.