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

The oxidation behavior of a K4169 superalloy was investigated over a temperature range of 800 degrees C to 1100 degrees 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 f 3.72 kJ.mol-1. At 800 degrees C and 900 degrees 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 degrees 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.