Effect of yttrium addition on microstructure and orientation of hydride precipitation in Zr-1Nb alloy

The purpose is to investigate the role of yttrium addition in improving hydride embrittlement resistance in Zr-1Nb alloy, because yttrium addition has been widely used to improve oxidation resistance of alloys. The results suggest that 0.2 wt.% yttrium addition can effectively lower hydrogen absorption in Zr-1Nb alloy. The microstructural characterization shows that the precipitated hydrides are interlinked to have a width of 200-600 nm and a shape of lamellar or “dendritic”. The electron backscattered diffraction (EBSD) results show that the crystallographic orientation relationship between precipitated hydrides and zirconium matrix is (0001)α-Zr//{111}δ-H0.62Zr0.38 or (0001)α-Zr//{100}δ-H0.62Zr0.38, depending on the position and morphology of hydrides. The depression of hydrogen absorption is attributed to the reduction of transgranular hydride precipitation by yttrium addition. This study provides an experimental basis for designing new zirconium alloys with enhanced hydrogen absorption resistance.