Study of Microstructure, Hydrogen Solubility, and Corrosion of Ta-Modified Zr-1Nb Alloys for Nuclear Applications

Modified Zr-1Nb alloys with Ta additions is a potential strategy to improve structural alloys for nuclear reactors. The effects of Ta on microstructural stability and resistance to corrosion of Zr-1Nb alloys were systematically investigated and elucidated. The (alpha + beta) microstructure in Zr-1.05Nb, Zr-0.85Nb-0.20Ta, and Zr-0.85Nb-0.40Ta (wt.%) alloys were obtained with the following two thermomechanical processes after a water quenching from beta Zr: (alpha) annealed at 570 degrees C for 3840 h and (b) a combination of intermediate annealing temperatures and cold rolled steps. Quantitative EDS-TEM analysis together with DSC measurements were used to characterise the changes in phase compositions and the fraction of beta-phase precipitates. Hydrogen solubility was measured in alloys with the first annealed condition. The Ta additions increase the monotectic transformation temperature, improves the steam corrosion at 400 degrees C and 10 MPa up to 14 days, and decreases slightly the hydrogen solubility. The higher thermal microstructural stability compared to Ta-free Zr-1Nb alloys provides potential advantages for increases in operating temperature or acceleration of precipitation kinetics during thermomechanical processing.