High-Temperature Oxidation Behavior of Al-Co-Cr-Ni-(Fe or Si) Multicomponent High-Entropy Alloys

High-entropy alloys (HEAs) are a class of alloys that are being considered for a number of applications. In the present study, the microstructures and 1050°C oxidation behaviors of two HEAs, Al 10 Cr 22.5 Co 22.5 Ni 22.5 Fe 22.5 (at.%) and Al 20 Cr 25 Co 25 Ni 25 Si 5 have been investigated along with Al 15 Cr 10 Co 35 Ni 35 Si 5 , which is a high-temperature shape-memory alloy. Oxide formation occurred via selective oxidation in a manner that was consistent with the oxide formation model devised by Giggins and Pettit for model Ni-Cr-Al alloys. The lower Al content alloy formed an external Cr 2 O 3 scale and an internal subscale consisting of Al 2 O 3 and AlN precipitates. The higher Al content alloys exhibited smaller mass gains and formed external Al 2 O 3 scales without any internal oxidation of the alloys.