Preferential precipitation of hydrides in textured zircaloy-4 sheets

Abstract

Cold-worked and stress relieved (CWSR) zircaloy-4 sheet-samples were charged with 45–247 wt. ppm of hydrogen using an electrolytic technique. Morphology and orientation of hydrides was examined with the help of optical microscopy (OM) and electron backscatter diffraction (EBSD) technique. The hydrides identified as δ-ZrH 1.5 phase by EBSD analysis, were located both within the grains and along the grain boundaries, but the grain boundary hydrides appeared to be dominant. The hydrides and the matrix have the (0 0 0 1)α-Zr//(1 1 1)δ-ZrH 1.5 orientation relationship at all locations. Three types of grain boundary hydrides were observed. A closer look on the grain boundary hydrides shows that the grain boundary hydrides are not exactly on the grain boundary; but very near the grain boundaries that follow the crystallographic relation (0 0 0 1)α-Zr//(1 1 1)δ-ZrH 1.5, only very few exceptions were recorded. The preferential sites for the grain boundary hydrides were basal planes of zirconium matrix located close to grain boundaries. Also, the hydrides shows strong {1 1 1} texture with maxima located at the same angle on the pole figure as the maxima of basal plane of α-zirconium matrix. The reproducibility of the results was verified using samples with different hydrogen concentrations.