A novel (CoFeNi)₈₂Ti₅Al₅V₈ medium entropy alloy showing an ultra yield strength and a good ductility by L1₂ nanoparticles strengthening and dislocation strengthening

This paper designed a novel (CoFeNi)₈₂Ti₅Al₅V₈ medium entropy alloy (MEA) with “fcc + L1₂” typical structure using JMatPro. The microstructure of the alloy, like recrystallization/non-recrystallization and L1₂ nanoparticle size, can be well controlled by thermal-mechanical processing. The result shows that the (CoFeNi)₈₂Ti₅Al₅V₈ MEA exhibits a good combination of ultra high yield strength of ∼1500 MPa and ultimate tensile strength of ∼1747 MPa with total ductility of ∼10.8 % when the volume fraction of non-recrystallized region with high-density L1₂ nanoparticles (∼46 nm) is up to ∼91 %. Here, the high volume fraction non-recrystallization region is along with the high-density dislocations (∼6.29 × 10¹⁴ m⁻²). Thus, the high strength of present MEA is mainly attributed to L1₂ nanoparticle precipitation strengthening and dislocation strengthening, which contributes ∼686 MPa and ∼305 MPa to the total yield strength (accounting for ∼66 %), respectively. Therefore, the idea of combining precipitation strengthening with dislocation strengthening offers a paradigm to develop advanced structural materials for modern industrial applications.