Effect of dissolved oxygen on the corrosion resistance of Zr-0.75Sn-0.35Fe-0.15Cr-0.3Nb alloy in 400 ℃ super-heated steam

Abstract:

In order to investigate the effect of dissolved oxygen ( DO ) on the super-heated steam corrosion of Zr-0.75Sn-0.35Fe-0.15Cr-0.3Nb ( wt% ) alloy, the samples were put into a static autoclave and a dynamic autoclave for 400 °C/10.3 MPa/deoxygenation and 300 ppb DO super-heated steam corrosion tests, respectively. The corrosion resistance of the alloy was evaluated by corrosion weight gains. Scanning electron microscope and transmission electron microscope were used to analyze the microstructure of the oxide film and the characteristics of the oxide film/metal (O/M) interface. The results reveal that DO can accelerate the corrosion of Zr-0.75Sn-0.35Fe-0.15Cr-0.3Nb alloy, and the weight gain after 250 d exposure under 300 ppb DO is 17 % higher than that under deoxygenation condition. The transition layer at the O/M interface under the deoxygenation condition is thinner than that under the 300 ppb DO condition. In addition, a ZrO layer of about 100 nm is observed in the transition layer under the former condition but not observed under the latter condition. To some extent, the thicker transition layer and the existence of the ZrO layer can provide more time for the stress release in the oxidation process, inhibiting the generation of cracks and thus improving the corrosion resistance of zirconium alloys. This can explain the better corrosion property in the later stage of corrosion under the deoxygenation condition.