The influence of Al addition and aluminizing process on oxidation performance of arc melted CoCrFeNi alloy

High entropy alloys are new promising alloys for high-temperature applications. Sluggish diffusion, which is one of their various important properties, contributes to their stability and oxidation resistance. Some Al-containing alloys and/or aluminized alloys have superior resistance due to the alumina layer forming on their surfaces during high-temperature oxidation. In this study, to see the effect of the Al-content and aluminizing process on a HEA, FCC structured -CoCrFeNi and BCC + B2 structured -CoCrFeNiAl alloys were produced by arc melting technique. The produced CoCrFeNi was aluminized at 700 °C for 4 h with the mixture of Al (40%), NH4Cl (20%) and Al2O3 40%. The surface of aluminized CoCrFeNi alloy was composed of Al-rich phases like diffusion aluminide coatings. Samples were exposed to isothermal oxidation tests at 950 °C for 5, 25, 50 h. SEM, EDS and XRD analysis results show that both Al addition and aluminizing process improved the oxidation performance of CoCrFeNi alloy. The formation of the Al2O3 layer resulted in lower mass gain during the oxidation tests while mixed oxides and Cr2O3 formations on the surface of CoCrFeNi led to higher mass gain. In addition, no dramatic difference was observed between the oxidation performance of CoCrFeNiAl and aluminized CoCrFeNi.