Oxidation behavior of Alloy 718 at a high temperature

The surface oxidation behavior of Alloy 718 is not well understood due to the chemical complexity of the alloy system. In this work, high temperature oxidation behavior of Alloy 718 in air at 1100 °C was investigated by varying the oxidation time up to 180 h. Three distinguished surface layers were observed depending on the oxidation time. Outside layer was single-phase Nb-rich Cr oxides with some voids and microcracks. The second layer had small amount of discontinuous phase (Al2O3). Both outside layer and second layer have often been observed in Ni-based superalloys. The third layer with complicate shapes of carbides was also observed in the present study. It was composed of the various (TixNby)C type carbides showing the different shape with the different ratio of x to y.