Oxidation Behaviour of New Nickel-Base Superalloys with Varying Aluminium: Niobium Ratio

New Ni-base superalloys with higher temperature capability are required for future, more efficient gas turbine engines. In designing such alloys, careful consideration is required of the elemental concentrations to ensure that a suitable balance of mechanical properties and environmental resistance is obtained. In this study, the oxidation resistance of a series of new Ni-base superalloys with varying Al:Nb ratio has been assessed through long-term exposures in air at elevated temperature. The oxide scale was characterised using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and quantitative measurements of oxide scale dimensions. The alloys were found to form continuous chromia scales at 700 °C and outperformed several current commercial superalloys. However, following exposure at 800 °C, significant microstructural degradation was observed due to precipitation of the δ phase.