Oxidation Behavior of Al sub(8)Co sub(17)Cr sub(1 7)Cu sub(8)Fe sub(17)Ni sub(33), Al sub(23)Co sub(15)Cr sub( 23)Cu sub(8)Fe sub(15)N i sub(15), and Al sub(17)Co sub(17)Cr sub( 17)Cu sub(17)Fe sub(17) Ni sub(17) Compositionally Complex Alloys (High-Entropy Alloys) at Elevated Temperatures in Air

Oxidation behavior of the compositionally complex alloys (high-entropy alloys) Al sub(8)Co sub(17)Cr sub(17)Cu sub(8)Fe sub(17)Ni sub(33) (fcc-alloy), Al sub(23)Co sub(15)Cr sub(23)Cu sub(8)Fe sub(15)Ni sub(15) (bcc-alloy), and Al sub(17)Co sub(17)Cr sub(17)Cu sub(17)Fe sub(17)Ni sub(17) (reference-alloy) at elevated temperatures in air is investigated. The microstructures of the oxide scales and the substrates are analyzed using scanning electron microscopy and X-ray diffraction. All oxidized alloys follow a parabolic kinetic law with low mass change per surface area at 800 degree C. The Al sub(8)Cr sub(17)Co sub(17) Cu sub(8)Fe sub(17)Ni sub(33) alloy follows sub-parabolic kinetic law at 1000 degree C and exhibits good oxidation resistance at both tested temperatures (800 and 1000 degree C). Two alloys, Al sub(23)Co sub(15)Cr sub(23)Cu sub(8)Fe sub(15)Ni sub(15) and Al sub(17)Co sub(17)Cr sub(17)Cu sub(17)Fe sub(17)Ni sub(17) suffer from strong spallation at 1000 degree C. High-temperature oxidation behavior for different kinds of high-entropy alloys has been highlighted. The oxidation behavior depends on the chemical composition of the alloy. The sufficient mole fraction of Al and Cr in the fcc-alloy enables the formation of both alumina- and chromia-protective scales. Only alumina scale formed in the bcc- and reference-alloys enhances the spallation at 1000 degree C.