Corrosion resistance of some alpha-dispersoid zirconium alloys in water vapour at 400°C and 500°C

Abstract

The corrosion of Zr, Zircaloy-4, Zr + 2.5 Nb, Zr +1.15 Cr + 0.1 Fe and experimental binary alloys of Zr with Cu, Ni, Fe and Cr was studied at 400 and 500°C in moist helium. The volume fraction of the second phase in the experimental alloys was approximately constant but the distribution and size of the second phase varied slightly from alloy to alloy. Nevertheless, the corrosion behaviour of the alloys was correlated with composition and solute distribution after corrosion, assuming similar metallurgical structures. No alloying addition significantly improves the corrosion resistance of pure Zr at 400oC though Ni and Cu improve it at 500°C. The order of increasing corrosion resistance prior to transition appears to follow the order of decreasing alloy solubility in the oxide film. The time to transition and corrosion rate after transition are also related to alloy solubility in the oxide film. Zircaloy-4, Zr + 2.5 Nb and Zr-Cr alloys may not be suitable for service in moist atmospheres at 400-500°C, whereas Zr-Cu, Zr-Fe and Zr-Ni alloys show superior corrosion resistance under these conditions.