Effect of Ti content on microstructure evolution and mechanical properties of FeCoNi-based medium-entropy alloys

In this study, we investigated the effect of Ti content on the microstructure, mechanical and damping properties of FeCoNi-based multi-principal element alloys. A series of as-cast (FeCoNi)_100-xTi_x medium-entropy alloys with different Ti contents were prepared using electric arc melting. The results show that the composition of (FeCoNi)_100-xTi_x medium-entropy alloy appears sequentially with increase in Ti contents as a single-phase FCC solid solution phase (γ), L1₂-(Ni, Co)₃Ti precipitated phase (γ'), HCP-structured Widmanstätten laths structure and HCP-Fe₂Ti-Laves phase. The strength of these alloys decreases after an initial rise due to an increase in the volume fraction of precipitated phases, the Widmanstätten laths structure and the Laves phases, while the ductility generally decreases. Among all samples, the (FeCoNi)₉₅Ti₅ alloy has balanced strength and ductility (tensile strength: ~ 840 MPa, elongation: ~ 25%) as well as good damping properties (Q⁻¹: ~ 0.04). This work provides rich data for the study of the formation of multiple phases and their mechanisms of action.