Influence of Cu content on high temperature oxidation behavior of AlCoCrCuxFeNi high entropy alloys (x=0; 0.5; 1)

Studies on the oxidation behavior of high entropy alloys from the Al-Co-Cr-Cu-Fe-Ni metallic system were conducted. Three different high entropy alloys were synthesized using arc-melting method: AlCoCrFeNi, AlCoCrCu0.5FeNi and AlCoCrCuFeNi, with their crystal structures being respectively BCC, BCC and BCC + FCC. All alloys were oxidized in the air atmosphere at temperature of 1273 K for different time periods. Basing on the thermogravimetric result, the oxidation rate of the materials decreased with the increase of Cu content and the values of parabolic constants were on the level similar to those observed in Ni-Al intermetallic alloys. In all cases the oxide scale consisted of alpha-Al2O3, which exhibited poor adhesion to the surface during the cooling process, what was especially visible in alloys with Cu addition. In all oxidized samples a tendency towards formation of the Al-depleted FCC phase directly beneath the scale was observed. The phase constitution of all materials changed significantly during the oxidation process, with multiple new phases appearing in the system. (C) 2016 Elsevier Ltd. All rights reserved.