Effect of annealing temperature on the structure and properties of FeCoCrNiMo high-entropy alloy

FeCoCrNiMo high-entropy alloy was melted by vacuum arc melting. The alloys were vacuum annealed at 873, 1,073, and 1,273 K, respectively. X-ray diffractometer (XRD), scanning electron microscope (SEM), simultaneous thermal analyzer, microhardness tester, and universal testing machine were used to study the microstructure, the thermal stability, hardness and compression mechanics of as-cast and annealed FeCoCrNiMo alloys. The results show that the alloy is composed of face-centered cubic (FCC) phase and σ phase in both as-cast and annealed states, and the σ phase and μ phase can maintain structural stability at 873 K annealing temperature. The μ phase decomposes to form the σ phase after annealing at 1,073 K, and part of the σ phase dissolves in the FCC phase when annealed at 1,273 K. Both the as-cast and annealed alloys have a typical dendritic structure. The σ phase is enriched in dendrites, and the FCC phase exists between the dendrites. The microstructure of the alloys in the annealed state is more refined than that of the alloy in the as-cast state. In the 1,073 K annealed state, the FeCoCrNiMo alloy has the highest hardness, yield strength, and fracture strength. The fracture mechanism of the alloy is intergranular brittle fracture and cleavage fracture.