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)_(97)Mo_(3)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)_(97)Mo_(3)alloy.Ab initio calculation results indicate the mean square atomic displacement(MSAD)and SFE value of(CoCrNi)_(97)Mo_(3)alloy is 42.6 pm^(2)and-40.4 mJ/m^(2)at 0 K,respectively.The relationship between mechanical properties and MSAD,SFE for various multiple principal element alloys is discussed.

Microstructural Evolution of Co_(35)Cr_(25)Fe_(30)Ni_(10) TRIP Complex Concentrated Alloy with the Addition of Minor Cu and Its Effect on Mechanical Properties

The influences of minor Cu addition(2 and 4 at.%)on the microstructural evolution and room-temperature mechanical property of metastable Co_(35)Cr_(25)Fe_(30)Ni_(10)are systemically investigated in the present study.The results indicate that the thermally induced hexagonal close-packed(HCP)phase is absent when Cu was added,due to the increase in stacking fault energy(SFE).The 2%-Cu-added alloys showed the largest total elongation of 69%among the three alloys.With the addition of Cu content reaching 4 at.%,heterogeneous grain structures composed of coarse grains(~9μm)and fine grains(~4μm)and Cu-rich precipitates near the grain boundary are observed,showing the highest yield strength.Additionally,the segregation state of Cu was quantitatively characterized by electron probe microanalysis(EPMA).And effects of Cu addition on microstructures and tensile properties of(Co_(35)Cr_(25)Fe_(30)Ni_(10))_(100-x) Cu _(x) are also discussed.The findings are beneficial to comprehensively understand the Cu-containing complex concentrated alloys.