Chromium-Dependent Effect on Oxidation Behavior of Ni-Fe-Based Superalloy for Ultra-Supercritical Steam Turbine Applications: Influence of Temperature and Pure Steam

Three Ni-Fe-based superalloys with 16 wt% to 18 wt% Cr were designed for steam turbine components in advanced ultra-supercritical power plants. The oxidation behavior of these alloys was evaluated at 750°C to 850°C for 1,000 h to explore the chromium-dependent effect on the oxidation behavior in static air and pure steam. The results reveal that the oxidation rate of the alloys decreased as the Cr content increased in both the air and steam environment. However, such a beneficial effect of Cr was found to be temperature-dependent, which became less significant when the exposure temperature increased from 750°C to 850°C, leading to the formation of an additional NiFe₂O₄ layer and severe internal Al₂O₃/TiO₂ oxide. The impact of temperature and pure steam on the oxidation resistance of the alloys were discussed based on the calculation of critical Cr concentration.