Isothermal oxidation behavior of a new Re-free nickel-based single-crystal superalloy at 950 °C

The isothermal oxidation behavior of a new Re-free nickel-based single-crystal superalloy in air at 950 °C for 200 h was studied by scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results indicate that oxidation kinetics obeys parabolic law approximately, and the mass gain increases rapidly during initial oxidation stage and then gradually slows down. The oxidation scales are composed of three layers: the outer layer mainly consists of NiO with a small amount of CoO; the intermediate layer is mainly composed of Cr2O3 with a small amount of spinel compounds such as CrTaO4, NiCr2O4, CoCrAl2O4, CoAl2O4, and NiAl2O4; and the inner layer is composed of A12O3. Inner Al2O3 layer suppresses the diffusion of elements between oxygen and alloy elements, slows down the alloy oxidation speed, and also suppresses the growth of the oxide scale and reduces the oxidation rate, which is agreeable with the oxidation kinetics.