Abstract
The microstructure, phase composition, and high-temperature oxidation resistance of Fe-free AlCoCrNiNb(0.2) and AlCoCr(0.5)NiNb(0.2) high-entropy alloys (HEAs) were investigated. In the as-cast HEAs, niobium was found to mainly release as a Laves phase in the interdendritic region, and its solubility in the dendrites of the BCC solid solution was about 2 at.%. Both samples exhibited parabolic behavior during 100 h oxidation at 1000 °C and 1100 °C. The AlCoCrNiNb(0.2) alloy demonstrated higher resistance to high-temperature oxidation compared to AlCoCr(0.5)NiNb(0.2). The specific weight changes after 100 h of isothermal holding at 1000 °C and 1100 °C were 0.65 mg/cm(2) and 1.31 mg/cm(2), respectively, which are superior compared to the Fe-containing HEAs. Cr was revealed to play an important role in the oxidation behavior of the HEAs, decreasing the parabolic oxidation rate constant and increasing the activation energy of the oxidation process in the alloys.