L12 nanoparticles-strengthened Co2Ni2Cr medium entropy alloy showing an outstanding tensile property

In this paper, we designed a new L12 nanoparticles-strengthened fcc-structured (Co2Ni2Cr)85Al7.5Ti7.5 MEA. The high-density L12 nanoparticles with an average size of ~57 nm are uniformly distributed in the grain with an average size of ~37 μm. The volume fraction of L12 nanoparticles is up to ~45%. The L12 nanoparticles can be identified as the (Ni,Co,Cr)3(Ti,Al) multi-component phase. Compared to the single-phase Co2Ni2Cr base alloy with a yield strength of ~208 MPa and an ultimate tensile strength of ~660 MPa, (Co2Ni2Cr)85Al7.5Ti7.5 MEA possesses a much higher yield strength of ~1125 MPa and an ultimate tensile strength of ~1540 MPa while retaining an excellent ductility of ~38%. The precipitation strengthening by L12 nanoparticles takes the largest contribution to the yield strength, and the contribution value is up to ~712 MPa. The deformation mode is dominated by mechanical twins for Co2Ni2Cr base alloy and (Co2Ni2Cr)85Al7.5Ti7.5 MEA, and the mechanical twins are more prevalent in the Co2Ni2Cr base alloy.