High-temperature oxidation behavior of Ni-Cr-W and Ni-Cr-Fe superalloys: A comparative study at 1000 °C

The oxidation behavior and mechanism of Ni-Cr-W based and Ni-Cr-Fe based superalloys were investigated through isothermal oxidation experiments in air at 1000 °C. The results indicate that the oxidation kinetics curves of both alloys generally follow a parabolic law, with the diffusion of ions in the oxide scale being the main controlling of the oxidation process. Despite the outer oxide scales of both alloys peel off after 300 h of oxidation, the inner oxide scales remain tightly intact and still maintain excellent oxidation resistance. The Ni-Cr-W-based and Ni-Cr-Fe-based superalloys exhibited weight gains of approximately 1.20 mg/cm² and 1.12 mg/cm², respectively. However, the presence of a dense and continuous Nb-rich layer within the oxide scale of Ni-Cr-Fe based superalloys promotes Cr₂O₃ formation, which further inhibits diffusion of other alloying elements and oxygen within the oxide scale. This also increases the bond strength between the oxide scale and matrix. Therefore, Ni-Cr-Fe based superalloys exhibit better oxidation resistance than Ni-Cr-W based superalloys in the later stages of oxidation. Additionally, the internal oxide Al₂O₃ particles are distributed along the grain boundaries of the alloy matrix, inhibiting the diffusion of other alloying elements and oxygen along the grain boundaries.