Effect of Al and Ti on High-Temperature Oxidation Behavior of CoCrFeNi-Based High-Entropy Alloys

CoCrFeNiAlxTiy high-entropy alloys were produced by the induction melting method and their oxidation behavior investigated when exposed to 1000°C for different durations. One or more body-centered cubic phases were found in all alloys, except CoCrFeNiTi0.5. In the CoCrFeNiTi0.5 alloy, two different face-centered cubic phases and one tetragonal sigma phase were detected. Scanning electron microscopy elemental analysis showed that all the alloys exhibited homogeneous microstructure. Energy-dispersive x-ray spectroscopy analysis revealed that Cr and Fe elements were enriched in one phase and Al-Ni-Ti elements in another. The presence of Ti negatively affected the oxidation behavior. According to the oxidation test results, dominant Al2O3 formation was observed in the CoCrFeNiAl0.5 and CoCrFeNiAlTi0.5 alloys. As a result, these two alloys exhibited the best performance among the five high-entropy alloys in terms of mass gain and oxide thickness.