Abstract
In order to discuss the role of chromium in the passivity of Fe–Cr and Ni–Cr alloys in a high temperature and high pressure water environment, the initial process of repassivation of newly created surface of these alloys has been analyzed by a straining electrode technique, and also the depth profile of the composition of films formed on these alloys in the same environment is examined by Auger electron spectroscopy.
It is observed that chromium addition simply increases the initial current density on bare surface of both the Fe–Cr and Ni–Cr alloys. The repassivation rate for the Fe–Cr alloys was enhanced by chromium addition of more than 8 mass%, but was rather retarded by the addition of 3 mass% chromium. On the other hand, the repassivation currents of the Ni–Cr alloys were increased by chromium addition and no promotion of repassivation rate was observed during the short period of the straining electrode test. Auger analysis showed that enrichment of chromium in the film occurred only for the high chromium Fe–Cr alloy, but no enrichment occurred for the low chromium Fe–Cr alloy and for all the Ni–Cr alloys. The contribution of the chromium addition to the repassivation behavior of the Fe–Cr and Ni–Cr alloys was discussed in consideration of the effect of chromium on the film composition.
