Oxidation behavior and mechanism of powder metallurgy Rene95 nickel based superalloy between 800 and 1000 °C

The oxidation behaviors of powder metallurgy (PM) Rene95 Ni-based superalloy in the temperature range of 800-1000 °C are investigated in air by virtue of isothermal oxidation testing, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the oxidation kinetics follows a square power law as the time extends at each temperature. The oxidation layers are detected to be composed of Cr₂O₃, TiO₂ and a small amount of NiCr₂O₄. The cross-sectional morphologies indicate that the oxidation layer consists of three parts: Cr-rich oxide layer, Cr and Ti duplex oxide layer, and oxidation affected zone. Theoretical analyses of oxidation kinetics and thicknesses of oxidation layers confirm that the activation energy of oxidation of PM Rene95 superalloy is 165.32 kJ mol⁻¹ and the oxidation process is controlled by diffusions of oxygen, Cr, and Ti. Accordingly, a diffusion-controlled mechanism is suggested to understand the oxidation behaviors of PM Rene95 superalloy at elevated temperatures.