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 °C, 600 °C, and 700 °C. Results indicate that Cr₂O₃ dominates as the primary oxide at 700 °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.