A study on the effects of dissolved hydrogen on zirconium alloys corrosion

The effects of dissolved hydrogen on oxide phase transformation and micro-structural changes during zirconium oxide growth were investigated using Raman spectroscopy and Transmission Electron Microscopy (TEM). Raman spectra measurements show that tetragonal zirconia develops during oxide growth and a fraction of the phase in pre-hydrided alloy is consistently lower than that of an un-hydrided one. This was observed identically in both Zircaloy-4 and Zr–1.5Nb alloys. TEM analysis at the metal-oxide interface support that the Raman spectra changes resulted from micro-structural changes. These results suggest that the dissolved hydrogen may cause meta-stabilization of the tetragonal phase oxide grown at the metal-oxide interface, probably by relaxing the compressive stress built up at the interface, or by modifying the stress distribution over the interface. The relaxation or modification possibly comes from the mitigation of the lattice incoherency between the metal and the oxide at the interface that is the origin of the compressive stress build-up.