Influence of Al content on high temperature oxidation behavior of AlxCoCrFeNiTi0.5 high entropy alloys

Studies on the oxidation behavior of high entropy alloys (HEAs) from the AlxCoCrFeNiTi0.5 (x = 0.5, 1.0, 1.5) metallic systems are conducted. In this work, the alloys are synthesized using arc-melting method, and the microstructure, anti-oxidant properties and oxidation products of the alloys at 700 °C, 900 °C and 1100 °C up to 100 h have been studied. The main substrate phases constitution in the arc-melted AlxCoCrFeNiTi0.5 HEAs was inter-dendritic FeCr-rich BCC1 and dendritic FeCr-poor BCC2 phases. With the increase of Al content, the fraction of the BCC2 phase increases while the BCC1 phase decreases, meanwhile the formation of FCC and σ inter-metallic phases are suppressed. At 700 °C −1100 °C, all alloys exhibit initial transient oxidation followed by various degrees of parabolic oxide growth; the Al1.5CoCrFeNiTi0.5 alloy exhibits excellent oxidation resistance because a continuous compact layer of (Al0.9Cr0.1)2O3 oxide films are produced on the alloy surface. The Kp values for the Al1.5CoCrFeNiTi0.5 alloy oxidized at 1100 °C for 100 h can be up to about 1.03×10−12 g2cm−4s−1.