Microstructure and mechanical properties of CoCrNi-Mo medium entropy alloys: Experiments and first-principle calculations

The effect of Mo additions on the microstructures and mechanical properties of CoCrNi alloys was investigated, meanwhile, ab initio calculations are performed to quantitatively evaluate the lattice distortion and stacking fault energy (SFE). The yield strength, ultimate tensile strength, and elongation of (CoCrNi)97Mo3 alloy are 475 MPa, 983 MPa and 69 %, respectively. The yield strength is increased by ∼30 % and high ductility is maintained, in comparison with CoCrNi alloy. Besides the nano-twins and dislocations, the higher density of stacking faults is induced during the tensile deformation for (CoCrNi)97Mo3 alloy. Ab initio calculation results indicate the mean square atomic displacement (MSAD) and SFE value of (CoCrNi)97Mo3 alloy is 42.6 pm2 and -40.4 mJ/m2 at 0 K, respectively. The relationship between mechanical properties and MSAD, SFE for various multiple principal element alloys is discussed.