Isothermal oxidation behavior of Ni-20Cr-18W superalloy at 1100°C

The isothermal oxidation behavior of a new Ni-Cr-W base superalloy Ni-20Cr-18W at 1100°C has been investigated by analytical electron microscopy, scanning electron microscope coupled with energy dispersive spectrum and X-ray diffraction. Oxidation kinetics was evaluated from measurements of mass change, metal loss and internal penetration. Initially, the mixtural oxide scale is composed of hexagonal Cr₂O₃, cubic NiO and spinel-type (Ni, Mn, Cr)₃O₄ isomorphous with M₃O₄ at the initial stage of oxidation. After long-term oxidation, the oxide scale turns from mono-layer to double-layer. There is a consecutive Cr₂O₃ scale at inner adherent layer, and a compact NiO scale at outer layer which can restrain the inner Cr₂O₃ volatilization. At the same time, the oxidation void has formed between the oxide scale and interface of the alloy (scale/metal interface), and the inner oxidation of Al element happens at this place.