Achieving Excellent High‐Temperature Oxidation Resistance in a Novel L1₂‐Reinforced Co‐Rich Medium‐Entropy Alloy

Excellent high‐temperature oxidation resistance for traditional high‐entropy alloys/medium‐entropy alloys (MEAs) is still a huge challenge. Herein, a novel Co 51.3 Ni 19.5 Cr 19 Al 6.4 Ti 3.4 Nb 0.4 MEA with superior high‐temperature oxidation resistance is designed. The specific high‐temperature oxidation behaviors of the studied MEA are systematically investigated at 800, 900, and 1000 °C for 200 h. Specifically, the studied MEA remains a single face‐centered cubic (FCC) phase after solution treatment under vacuum at 1200 °C for 15 h, while high‐density L1 2 nanoprecipitates form inside the FCC matrix after aging treatment under vacuum at 750 °C for 12 h, revealing the consistency between the experimental results and the theoretical prediction. The results of oxidation tests indicate that the studied MEA with FCC matrix and L1 2 nanoprecipitates exhibits a superior oxidation resistance. The oxidation kinetics of the oxide layer follow a parabolic law at oxidation temperature of 800, 900, and 1000 °C and the corresponding oxidation rate constants ( k p ) are 0.001, 0.011, and 0.047 mg 2 cm −4 h −1 , respectively. The diffusion activation energy of the studied MEA is determined to be 258 kJ mol −1 and the oxidation process is controlled by outward diffusion of metallic elements and inward diffusion of oxygen. The research results provide guidance for the development of superalloys.