Oxidation behavior of high Hf nickel-based superalloy in air at 900, 1000 and 1100°C

To investigate the oxidation behavior of a nickel-based superalloy with high hafnium content (1.34wt%), this study performed isothermal oxidation tests at 900, 1000, and 1100°C for up to 200 h. X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy were applied to study the oxidation behavior. The weight gain of the high Hf nickel-based superalloy exhibited a parabola-like curve, and no spallation of the oxide scale was observed during the oxidation tests. The alloy presented excellent oxidation resistance, and no HfO₂ was observed in the oxide scale at 900°C. With the increase of the oxidation temperature to 1000°C, HfO₂ particles formed in the spinel phases of the scale, and “peg-like” HfO₂ was observed within and beneath the inner layer of Al₂O₃ after 200 h. As the oxidation temperature rose to 1100°C, “peg-like” HfO₂ was observed at the early stage of the oxidation test (within 25 h). The formation mechanism of HfO₂ and its impact on oxidation resistance were investigated based on the analysis of the oxidation test results at different temperatures.