Isothermal High-Temperature Oxidation Behaviour of Nickel-Based Superalloy IN740H

The isothermal oxidation behaviour of IN740H alloy was studied by conducting experiments in a thermogravimetric analyser in the presence of air and synthetic flue gas in the temperature range of 760–900 °C. SEM/XRD/EPMA/Raman spectroscopy was used for analysing surfaces/cross sections of oxidized/corroded specimens. The oxide layer consists of Ti-doped Cr₂O₃ and NiCr₂O₄ in air-oxidized specimens, whereas additional NiO and NiS form in the presence of flue gas at 900 °C. Alumina forms at the oxide/matrix interface and at 900 °C; it was followed by γ′ denuded zone with dispersed (Ti, Nb)C. The kinetics of oxidation in a steady state are found to be sub-parabolic for all the conditions.