Microstructure and mechanical properties of multi-principal component CoCrNiMo medium entropy alloys

In traditional high entropy alloy (HEA) systems, achieving a synergistic enhancement of alloy strength and ductility remains a challenge. However, dual-phase high entropy alloys, with their simultaneous high strength and high ductility, have shown potential for industrial applications. In this study, three multi-principal element CoCrNiMo alloys were synthesized by adding varying amounts of Mo to the base medium entropy Co45Cr27Ni28 alloy, which possesses a single face-centered cubic (FCC) phase. The impact of variations in Mo content on the alloy's microstructure and mechanical properties was investigated. Experimental data revealed that all three alloys formed dual-phase (FCC + mu) precipitation-strengthened medium entropy alloys (MEAs), where the mu phase is enriched with Mo, and its quantity increases with the increase in Mo content. With the rise in Mo content, the alloy's hardness increased from 240 +/- 20 HV to 668 +/- 35 HV, and tensile strength also increased, albeit at the cost of reduced plasticity. The single-phase medium entropy Co45Cr27Ni28 alloy exhibited a tensile strength and elongation rate of 591 +/- 15 MPa and 44 +/- 3%, respectively. The tensile strength of the dual-phase CoCrNiMo HEAs could be elevated to 857 +/- 16 MPa and 1045 +/- 25 MPa, while maintaining considerable elongation rates of 16 +/- 2% and 5 +/- 1%, respectively. This work provides a pathway for strengthening CoCrNi alloys and contributes positively to the development of high-performance HEAs.