Effect of hydrogenation on microstructure and mechanical properties of new zirconium alloy

Abstract

The zirconium alloy was thermo-hydrogen processed with 0.02 wt% and 0.2 wt% hydrogen, and the impact of hydrogen content on the microstructure and mechanical properties of the alloy was investigated. The hydrides in the hydrogen-treated alloys were identified as δ-ZrH_1.66, which exhibit a semi-coherent boundary with the α-Zr matrix and an orientation relationship of (0001)_α-Zr//(111)_δ. The hydride platelets tend to align in lines parallel to the rolling direction (RD) and transverse direction (TD) at a slow cooling rate after thermo-hydrogenation. Thermo-hydrogen processing introduced additional intragranular secondary phases characterized as larger-sized ZrFe₂ compared to those present in the raw alloy. The tensile strength and elongation of the zirconium alloys decrease with increasing hydrogen content due to the elevated hardness and brittleness of the hydrides. Specifically, the tensile strength decreases from 476 MPa without hydrogen to 449 MPa with 200 ppm hydrogen and 433 MPa with 2000 ppm hydrogen. The elongation of specimens without hydrogen was 38.4 %, whereas specimens with 200 ppm and 2000 ppm hydrogen exhibited reductions of 6.3 % and 42.7 %, respectively. Specimens with 2000 ppm hydrogen exhibited significantly low elongation due to the increased quantity and size of hydride lines.