Oxidation behavior of a Ni-Cr-Fe superalloy from 800 ℃ to 1100 ℃ in air: Formation and mechanism of multilayer oxide films

The oxidation behavior of a K4169 superalloy was investigated over a temperature range of 800 °C to 1100 °C in air for 100 hours. The formation of oxide film was analyzed using multiscale characterization techniques. The results show that the oxidation kinetics followed the parabolic law, with an oxidation activation energy of 234.59 ± 3.72 kJ∙mol⁻¹. At 800 °C and 900 °C, a double oxide layer formed, comprising an outer layer of Cr₂O₃ with minor TiO₂ and NiCr₂O₄ mixed oxides, and an inner layer of Al₂O₃. At temperatures above 1000 °C, the structure of the outer and inner layers remained unchanged, and a new intermediate layer appeared, primarily consisting of an Nb-rich layer and TiO₂. The formation of the multilayer oxide structure was attributed to the competing mechanisms of external diffusion of alloying elements through the matrix and internal diffusion of oxygen. With prolonged oxidation, the continuous diffusion of Ti destroyed the continuous and protective Cr₂O₃ layer, while Al absorbed incoming oxygen, forming fibrous A1₂O₃ that hindered further oxygen diffusion into the alloy matrix. The impact of oxidation time on oxide scale formation was similar to that of temperature, both leading to a thicker oxidation layer and the degradation of protective layers.