Mechanism of early oxide film evolution in typical nickel-based alloys in supercritical water at different temperatures

This study examines early oxidation in nickel-based alloys exposed to supercritical water (SCW) at 400 degrees C, 600 degrees C, and 700 degrees C. Results indicate that Cr2O3 dominates as the primary oxide at 700 degrees C, forming a robust barrier against spinel oxide growth. Lower temperatures favor mixed oxide formation, while higher temperatures result in Cr2O3-dominated layers due to preferential ion transport. At elevated temperatures, the primary alloying element involved in atomic cation interstitial generation shifts from Ni and Fe to Cr. The point defect model provides an atomic-scale understanding of the early oxide film formation mechanism.