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

Oxidation behavior of the compositionally complex alloys (high‐entropy alloys) Al 8 Co 17 Cr 17 Cu 8 Fe 17 Ni 33 (fcc‐alloy), Al 23 Co 15 Cr 23 Cu 8 Fe 15 Ni 15 (bcc‐alloy), and Al 17 Co 17 Cr 17 Cu 17 Fe 17 Ni 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 °C. The Al 8 Cr 17 Co 17 Cu 8 Fe 17 Ni 33 alloy follows sub‐parabolic kinetic law at 1 000 °C and exhibits good oxidation resistance at both tested temperatures (800 and 1 000 °C). Two alloys, Al 23 Co 15 Cr 23 Cu 8 Fe 15 Ni 15 and Al 17 Co 17 Cr 17 Cu 17 Fe 17 Ni 17 suffer from strong spallation at 1 000 °C.