Investigating Oxide Formation and Growth in Inconel 718 Oxidized at High Temperatures

In this study, oxide formation and growth in Inconel 718 oxidized at 1,000 °C and 1,100 °C were investigated using scanning electron microscopy and phase diagrams including oxygen partial pressure. Inconel 718 showed significantly improved oxidation resistance compared to that of Nickel 201 with no alloying elements. The oxide layer of Inconel 718 consisted of a Cr-rich upper layer and Nb-rich lower layer. In addition, the oxide layer of Inconel 718 at 1,100 °C was significantly Ti-enriched. NiO crystals were found to be oxidized on Nickel 201, which were grown long in the thickness direction, whereas the oxide layer composed of fine and equiaxed Cr 2 O 3 crystals was observed in the case of Inconel 718. Based on the phase diagram plotted for the oxygen partial pressure, primary Cr 2 O 3 , secondary Nb 2 O, and Nb 2 O 5 were followed by spinel oxide formation in Inconel 718.