Microstructure And Properties Of CoCrFeNiCu_xTi_0.3 High Entropy Alloys

In this paper,three kinds of multi-primary alloys CoCrFeNiCu_0.5Ti_0.3,CoCrFeNiCuTi_0.3 and CoCrFeCuCu_1.5Ti_0.3 are designed according to the composition design criteria of multi-principal high entropy alloys.The alloy ingots are made in a vacuum arc furnace and then alloyed.Long-term aging treatment at the same temperature.Scanning electron microscopy was used to observe the microstructure of the alloy.The micro-composition analysis was performed by using energy spectrum.The phase structure of the alloy was measured by X-ray diffractometer.The hardness and compressibility of the alloy were also tested.ItwasfoundthatCoCrFeNiCu_0.5Ti_0.3,CoCrFeNiCuTi_0.3,and CoCrFeNiCu_1.5Ti_0.3 multi-primary alloys all consist of FCC phases.When the molar ratio of Cu atoms increases,the FCC reaction peak shifts to the left,indicating that the lattice constant increases slightly.The main microstructure is the dendrite structure.When the content of Cu increases,Cu produces a segregation effect and concentrates in the intercrystalline region.According to the hardness test results of the alloy,the hardness of the alloy showed a decreasing trend from 286 HV to 249HV.The compressive strengths of CoCrFeNiCu_0.5Ti_0.3,CoCrFeNiCuTi_0.3 and CoCrFeNiCu_1.5Ti_0.3 are 1698 MPa,1680 MPa and 1416 MPa,respectively,and the plastic strain values are 50%,46%and 45%,respectively.CoCrFeNiCuTi_0.3 was aged for a long time and aged at 750?.for 100h,200h,300h,400h,500h,600h,700h,800h,900h,and 1000h,respectively.CoCrFeNiCuTi_0.3 changes from a single FCC phase to a mixture of FCC phase and a simple cubic phase.The content of simple cubic phase increases with the increase of treatment time.The dendritic structure changes from dendrite to a mixture of dendritic and lamellae.The dendrite structure is similar to that of the as-cast dendritic structure.The lamellar is composed of Ti,Ni,and Co.The layers are mainly composed of Co,Cr,Fe and Ni and Ti as well.According to the hardness test results of the treated alloy,the hardness value decreased from 347.02 HV to 269.69HV as the heat treatment time increased.The compressive strength decreased from2160MPa to 1792MPa,and the plastic strain value declined from 39%to 30%.The phase formation of this series of alloys is predicted and calculated.The results show that the mixed crucibles of CoCrFeNiCu_xTi_0.3 multi-primary alloys,the difference in atomic radius and the entropy of mixing are within a reasonable range of the formation of a stable solid solution phase.The valence electron concentration and electronegativity difference of CoCrFeNiCuxTi0.3 alloy system are 0.58,0.63 and0.69,and the FCC phase structure and simple cubic phase are within the alloy.