High-temperature air-oxidation of NiCoCrAlx medium-entropy alloys

Abstract

The oxidation behaviour of four NiCoCrAlx medium-entropy alloys (x = 0, 0.1, 0.3, or 0.5 mol.) was investigated in dry air at 600-900 degrees C. The oxidation kinetics of all the alloys followed the parabolic rate law at T >= 700 degrees C, and the oxidation rates increased with an increase in temperature and a decrease in Al content. Discontinuous oxide granules were formed on all the alloys at 600 degrees C, while complex scales were detected, strongly depending on the Al content and temperature. Internal attack of AlN precipitates was also observed for Al-containing alloys at T >= 700 degrees C.