EBSD studies on microstructure and crystallographic orientation of δ-hydrides in Zircaloy-4, Zr–1% Nb and Zr–2.5% Nb

The Zr–Nb alloys are reported to be showing superior resistance to corrosion and substantially lower hydrogen pickup when compared with Zircaloy. In the present study Zircaloy-4, Zr–2.5Nb and Zr–1Nb (E110) alloys were hydrided using high pressure hydrogen gas furnace at a pressure of 20 MPa. Hydriding was done by thermal cycling on the samples at a temperature of 350 °C for 10 cycles with 5 h soaking time. The microstructural observations on Zircaloy-4 and Zr–2.5Nb samples show long and interlinked hydride like chains, oriented along the circumferential direction. Whereas, in Zr–1Nb (E110) hydrides were short, thick without any preferential orientation with respect to the sample reference direction. Electron backscatter diffraction (EBSD) map shows the presence of β1 phase in two phased Zr–1Nb, Zr–2.5Nb samples. Heavy { 1     0     1 ¯     2 } 1     0     1 ¯     1 ¯ tensile twins and { 1     0     1 ¯     1 } 1     0     1 ¯     2 compression twins were observed in Zr–1Nb. Hydrides in Zircaloy-4 and Zr–2.5Nb have shown (0 0 0 1)α-Zr//{1 1 1}-ZrH1.5 orientation with α-matrix whereas almost 50% of hydrides in Zr–1Nb (E110) alloy are showing (0 0 0 1) α-Zr//{1 0 0} δ-ZrH1.5 crystallographic relation. The (0 0 0 1)α-Zr//{1 0 0}δ-ZrH1.5 orientation of hydrides in Zr–1Nb (E110) is observed for the hydrides formed at the twin boundaries.