Effects of Cr and Al Contents on the Oxide Structures of Ni-Based Superalloys at High Temperatures

In this study, the morphology of high-temperature surface oxides in Ni-based superalloys was investigated as a function of Cr and Al content. First, the oxide layer morphologies of various alloys published in the literature were classified according to the basic model of Cr and Al content. Then, the high-temperature oxide layers of high-Cr/low-Al and low-Cr/high-Al alloys were investigated using SEM/EDX mapping. The high-temperature oxidation of Ni-based superalloys is affected by the amount of added elements such as Ti, Cr, and Al. The oxidation rate of each element is NiO > TiO2 > Cr2O3 > Al2O3, and the shape of the surface oxide layer is determined by the oxidation rate. The oxide layer is mainly classified according to the flat and fibrous shapes of Cr2O3 and Al2O3 on the outermost layer. In this study, IN738LC and IN792, as the high Cr-low Al alloys, were found to have flat Cr2O3 and fibrous type Al2O3 in the outermost layer after long-term exposure to high temperatures, while CM247LC and CMSX4 which are the low Cr-high Al alloys were found to have flat type Al2O3 in the outermost layer after long-term exposure to high temperatures, which is in good agreement with the results of various literature on oxide layers on Ni-based superalloys.