Microstructure and Oxidation Behaviors of (TiVCr)2AlC MAX-Phase Coatings Prepared by Magnetron Sputtering

A solid solution is an effective approach to regulate the microstructure and hence the various properties such as hardness and oxidation behavior of materials. In this study, an M-site solid-solution medium-entropy-alloy MAX-phase coating (TiVCr)2AlC was prepared through combining the magnetron sputter deposition at low- and high-temperature vacuum annealing. The mechanical properties and high-temperature oxidation resistance in the 700–1000 °C temperature range in air of these coatings were then evaluated. The results showed that the 211-MAX-phase can be formed in the 700 °C vacuum for 3 h, and the crystallinity depended on the annealing temperature. Compared to the amorphous coating, the MAX-phase sample demonstrated superior oxidation resistance in terms of the onset temperature of the oxidation and the oxidation products. During high-temperature oxidation, a mixed oxide layer containing V2O5, TiO2, and Cr2O3 was formed at 700 °C on the surface of an amorphous coating, whereas only a thin continuous Al2O3 scale was observed at ≤800 °C for the crystalline (TiVCr)2AlC coating. Additionally, the maximum hardness of the coating reached 18 GPa after annealing. These results demonstrate the application potential of the medium-entropy-alloy MAX-phase coating in extreme environments such as aerospace, nuclear energy, and other fields.