High-temperature Oxidation Behaviour of AlxFeCrCoNi and AlTiVCr Compositionally Complex Alloys

Compositionally complex alloys (CCAs), also termed as high entropy alloys (HEAs) or multi-principal element alloys (MPEAs), are being considered as a potential solution for many energy-related applications comprising extreme environments and temperatures. Herein, a review of the pertinent literature is performed in conjunction with original works characterising the oxidation behaviour of two diverse Al-containing alloys; namely a lightweight (5.06 g/cm 3 ) single-phase AlTiVCr CCA and a multiple-phase Al 0.9 FeCrCoNi CCA (6.9 g/cm 3 ). The thermogravimetric results obtained during oxidation of the alloys at 700 and 900 °C revealed that both alloys tended to obey the desired parabolic rate law. Post-exposure analysis by means of electron microscopy indicated that while the oxide scale formed on the AlTiVCr is adherent to the substrate, the scale developed on the Al 0.9 FeCrCoNi displays a notable spalling propensity. This study highlights the need for tailoring the protective properties of the oxide scale formed on the surface of the CCAs.