Temperature-Dependent Isothermal Oxidation Behavior of a Ni-20Cr-18W Superalloy in Static Air

The oxidation behavior of superalloys has attracted more attention due to the increasing service temperature of components in aero-engines. In this study, the isothermal oxidation behavior of a Ni-20Cr-18W superalloy has been investigated at 900 and 1000 °C in air. The oxidation kinetics follows a parabolic oxidation law at both temperatures. The outer layer of the oxide scales is mainly composed of mixed oxides of Cr₂O₃ and NiCr₂O₄, and the inner layer is Cr₂O₃ at 900 °C. During oxidizing at 1000 °C, the oxide scales evolve from dense Cr₂O₃ single-layer structure to double-layer structure which consists of inner Cr₂O₃ layer and outer layer composed of lots of NiCr₂O₄, Cr₂O₃ and a small amount of NiO, and the size and content of NiCr₂O₄ are relatively larger than that of 900 °C. The internal oxidation zone dispersed with Al₂O₃ is formed under the oxide scales at both 900 and 1000 °C. The obvious cracks are observed at the interface between the outer layer and the inner layer, which is ascribed to the generation of growth stress and thermal stress. Compared with the oxidation behavior at 900 °C, the cracking and spalling in oxide scales are much severer at 1000 °C due to the greater internal stress. The experimental Ni-20Cr-18W superalloy is oxidized through the inward diffusion of oxygen and the outward diffusion of metal elements.