The effect of pressure on hydrogen solubility in Zircaloy-4

Abstract

The effect of pressure on the room temperature solubility of hydrogen in Zircaloy-4 was examined using synchrotron X-ray diffraction on small ground flake samples in a diamond anvil cell at pressures up to 20.9 GPa. Different combinations of hydrogen level/state in the sample and of pressure transmitting medium were examined; in all three cases examined, it could be concluded that pressure resulted in the dissolution of d hydrides and that interstitial hydrogen retards the formation of w Zr. A pressure of around 9 GPa was required to halve the hydride fraction. These results imply that the effect of pressure is thermodynamically analogous to that of increasing temperature, but that the effect is small. The results are consistent with the volume per Zr atom of the a, d and w phases, with the bulk moduli of a and d, and with previous measurements of the hydrogen site molar volumes in the a and d phases. The results are interpreted in terms of their implication for our understanding of the driving forces for hydride precipitation at crack tips, which are in a region of hydrostatic tensile stress on the order of 1.5 GPa.