Effect of Fe content on microstructure and mechanical properties of Al0·5CoCrFexNiTi0.5 high-entropy alloys

In this study, Al0.5CoCrFexNiTi0.5 alloys (where the molar ratio (x) is 0.5, 1.0, 1.5, and 2.0) were synthesized to elucidate the effect of their Fe content on their microstructure and mechanical properties. The results show that both Al0.5CoCrFe0.5NiTi0.5 and Al0.5CoCrFe1.0NiTi0.5 alloys consist of four phases, BCC, FCC, σ, and ordered BCC phases. The number of phases decreases to three for the Al0.5CoCrFe1.5NiTi0.5 and Al0.5CoCrFe2.0NiTi0.5 alloys, both of which consist of the FCC, BCC, and ordered BCC phases. The hardness of the alloys decreases from HV748 to HV399 with increasing Fe content. This result shows that addition of Fe to the alloy inhibits the formation of the σ phase while promoting the formation of the FCC phase, and thus indicates that Fe stabilizes the FCC phase. Al0.5CoCrFe0.5NiTi0.5, Al0.5CoCrFe1.0NiTi0.5, and Al0.5CoCrFe1.5NiTi0.5 alloys have a dendritic structure. However, the microstructure of the Al0.5CoCrFe2.0NiTi0.5 alloy changes into a three-phase eutectic structure. The compressive strength (σmax) of the alloys decreases with increasing Fe content. Accordingly, σmax decreases from 2240 to 1736 MPa, and the fracture strain increases from 0.11 to 0.45 as the Fe content increases from 0.5 to 2.0. Both Al0.5CoCrFe1.5NiTi0.5 and Al0.5CoCrFe2.0NiTi0.5 alloys exhibit high strength and high ductility.