Corrosion and oxide characteristics of Zr–1.5Nb–0.4Sn–0.2Fe–0.1Cr alloys in 360 °C pure water and LiOH solution

Abstract

Corrosion behavior of Zr–1.5Nb–0.4Sn–0.2Fe–0.1Cr (HANA-4) and Zircaloy-4 was investigated in 360 °C pure water and in 360 °C water containing 70 ppm Li. HANA-4 showed a much better corrosion resistance than Zircaloy-4 in pure water and maintained a lower corrosion rate even in LiOH solution where Zircaloy-4 showed an accelerated corrosion behavior. The oxide was characterized by an optical microscopy and a transmission electron microscopy. The oxide formed on HANA-4 in pure water was observed to have a layered structure with a smaller total oxide thickness for the same corrosion period, a higher layer thickness and a larger columnar grain size in the interface region when compared to Zircaloy-4. The oxide protectiveness of HANA-4 was also effective in maintaining a lower corrosion rate even in LiOH solution where a layered structure was not developed in the oxide of Zircaloy-4. This demonstrates that the oxide of HANA-4 was protective enough to prevent it from becoming porous by an ingress of Li + or LiOH.