First-principles and experimental study on structure and properties of CuCrCoFeNixTi high entropy alloy

CuCrCoFeNixTi(x = 0, 0.5, 1, 1.5, 2.0) high entropy alloys (HEAs) were designed and the solid solution structure model were established based on the first principles. Lattice constant, phase structure, elastic properties, state density and differential charge density of the HEAs were obtained. The simulation results show that the heat of formation of the alloys are negative. With the increases of Ni content, the density of HEA increases, the lattice constant decreases, the Poisson ratio increases, the G/B value decreases and the Cauchy pressure increases. It indicates that the HEAs change from brittleness to toughness. The differential charge density maps show that the charge distributions in the HEAs are relatively uniform, and the metal bond characteristics are presented. The state density diagrams show that CuCrCoFeNi₂Ti has the highest peak state density, which indicates that its metal properties are higher and its toughness is better. Finally, the CuCrCoFeNi_xTi HEAs were prepared by vacuum arc melting and the homogenization was carried out. The microstructures of the alloys were observed and the compression tests were conducted. The results show that the XRD patterns obtained by experiment are similar to those of simulation, and CuCrCoFeNi_xTi HEAs are mainly composed of FCC phase structure. As the Ni content increases, the microstructures of HEAs were more homogeneous, the compressive strength increased from 710.3 MPa to 1878.5 MPa, and the elongation rate increased from 4.9 % to 14.7 %. The fracture morphologies of CuCrCoFeNi_xTi HEAs present a quasi-cleavage fracture, which are mainly manifested in cleavage steps and tearing edges.