Corrosion Behavior of 90Nb-10Zr Alloy in 500 degrees C Super-Heated Steam

In order to further study the corrosion behavior of beta-Nb second phase particles (SPPs) in zirconium alloys, a bulk 90Nb-10Zr alloy was prepared by vacuum non-consumable arc furnace based on the chemical composition and crystal structure of beta-Nb SPPs. The 90Nb-10Zr alloy was corroded in super-heated steam at 500 degrees C and 10.3 MPa in a static autoclave for 1 and 7 h. The microstructure of the oxide film formed on the alloy was characterized by XRD, SEM and TEM. The results show that the monoclinic Nb2O5 is formed directly when 90Nb-10Zr alloy is corroded for 1 h, because the corrosion medium is directly contacted with the outer surface of the alloy. When 90Nb-10Zr alloy is corroded for 7 h, the oxide film on the alloy is double-layer structure: the outer layer is m-Nb2O5 and the inner layer is t-NbO2 since the occurrence of further corrosion requires the internal diffusion of the oxidizing substances in the corrosion medium. No single oxide of Zr is detected in this study. This oxidation process can reasonably explain the relationship between the corrosion behavior of Nb-containing zirconium alloy in super-heated steam and the Nb content.