Fundamental study on the corrosion mechanism of Zr-0.2Fe, Zr-0.2Cr, and Zr-0.1Fe-0.1Cr alloys

Corrosion and hydrogen pickup properties were investigated on sheet materials of pure Zr, Zr-0.2 wt%Fe, Zr-0.2 wt%Cr, and Zr-0.1 wt%Fe-0.1 wt%Cr which were given an intermediate anneal of 853 K or 1003 K, and a final anneal at 853 K. To clarify the substantial effects of iron and chromium, impurities were minimized by using crystal bar zirconium and pure alloy additions. Corrosion results in 633 K water showed that Zr had the lowest corrosion resistance and that Zr-0.1Fe-0.1Cr alloy heat treated at 1003 K had the highest. The alloys heat-treated at 1003 K showed higher corrosion resistance that those treated at 853 K for each composition except che Zr-0.2Fe alloy. Zr-0.2Fe alloys had higher hydrogen pickup ratios (80%) than those of Zr-0.2Cr and Zr-0.1Fe-0.1Cr alloys (10 to 20%). TEM and HR-SEM examination of oxide cross sections was also performed. Zr-0.1Fe-0.1Cr alloy formed columnar oxide grains with few fine cracks, while Zr and Zr-0.2Cr alloys had fine-equiaxed grains. Zr-0.2Fe alloys formed columnar oxide grains and included many lateral cracks. The corrosion mechanism of the alloys was associated with the electrochemical characteristics of the precipitates in this study.