High-temperature oxidation behaviour of AlxFeCrCoNi and AlTiVCr compositionally complex alloys

Abstract

Compositionally complex alloys (CCAs), also termed as high entropy alloys (HEAs) or multiprincipal element alloys (MPEAs), are being considered as a potential solution for many energyrelated 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 "opposing" alloys; namely a lightweight (5.06 g/cm 3 ) single-phase AlTiVCr CCA and a multiple-phase Al0.9FeCrCoNi CCA (6.9 g/cm 3 ). The thermogravimetric results obtained during oxidation of the alloys at 700 and 900°C revealed that while AlTiVCr revealed linear oxidation, Al0.9FeCrCoNi tended to obey the desired parabolic rate law. However, postexposure 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 Al0.9FeCrCoNi 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.