Microstructural evolution, mechanical and corrosion behaviors of as-annealed CoCrFeNiMox (x = 0, 0.2, 0.5, 0.8, 1) high entropy alloys

The CoCrFeNiMox high-entropy alloys (HEAs) (x = 0, 0.2, 0.5, 0.8, 1) are prepared by using an arc melting plus homogenization annealing method. The microstructural evolution, mechanical properties and corrosion resistance in seawater solution of the as-annealed HEAs are investigated. The results show that a new face-centered cubic (FCC’) phase precipitates from FCC matrix for the as-annealed Mo0.2 HEA. Compare with as-cast Mo0.2 HEA, the annealing induces the precipitation of σ phase from FCC’ phase. Besides the formation of σ phase surrounded by nano-size μ phase, a new σ′ phase formation is promoted by annealing treatment for HEAs with x = 0.8 and 1. The synergistic effects of serious lattice distortion and precipitation enhancement are dominant mechanisms responsible for the enhanced microhardness for as-annealed HEAs with Mo addition. The as-annealed HEAs with x = 0.8 and 1 show a serious embrittlement characteristic, mainly owing to the precipitation of σ′ phase with large quantity and coarsening size. The as-annealed CoCrFeNiMo0.5 HEA possesses excellent comprehensive corrosion resistance. Appropriate Mo content makes passive film denser, and brings down the overall dissolution rate.