## 1 Introduction  
High-entropy alloys (HEAs) have stimulated widespread interest due to their outstanding properties since they were independently proposed by [PERSON] and [PERSON] [1, 2]. In general, HEAs are composed of four or more principal elements in equal or similar molar ratios, and the percentage range of each element is 5-35 at.%. HEAs have a high entropy of mixing. Lattice distortion [3], cocktail [4], and sluggish diffusion effects [5] in HEAs have also been reported. HEAs are a single-phase random solid solution. For example, CoCrFeNi HEAs [1] have a FCC structure. MoNbTaV refractory HEAs [6] have a body-centered cubic (BCC) structure. At present, some important works have shown that HEAs have many excellent mechanical properties, such as high strength, wear resistance, high hardness, and high-temperature oxidation resistance and corrosion resistance [7, 8, 6]. For Co-Cr-Fe-Ni HEAs, there have been plenty of investigations on phase stability [9, 10, 11], local chemical ordering [12, 13], mechanical [14, 15, 16, 17, 18], tribological [19, 20, 21], corrosion [22, 23, 24, 25, 26, 27], and magnetic [28, 29] and irradiation resistance [30, 31]. Most of these works are based on experimental observations. For example, the metastable BCC phase appears in the rapid solidification microstructure along with the primary FCC phase [9]. At a low temperature, the combined effect of deformation twinning and phase transformation led to an increase in the strength of CoCrFeNi HEAs [15]. At a high temperature, CoCrFeNi HEAs have excellent wear resistance in a vacuum compared with steel and Ni-based intermetallic materials [19]. CoCrFeNi HEAs exhibit high strength and ductility due to stacking faults at a higher strain rate [18]. The addition of Al, Cu, Sn, Nb, and Mo to CoCrFeNi HEAs forms a stable oxide film to improve the corrosion resistance of the alloy in chloride solutions [22; 23; 26; 27]. The magnetic properties of CoCrFeNi indicate that it is a poor candidate for soft magnetic applications at a high temperature, but cold rolling will increase the magnetic entropy change [28]. Decreasing the Cr content in alloys led to an increase in the saturation magnetization or the Curie temperature of alloys [28]. First-principle calculations based on density functional theory (DFT) are also widely used in the study of HEAs' structure and properties. CoCrFeNi alloy undergoes structural phase transition from FCC to hexagonal close-packed (HCP) at 13.5 GPa [32]. Based on the Gibbs free energy, the energy difference between the FCC and HCP structures of CoCrFeNi alloy is very small, but its phase transition pressure can be changed from 1 GPa at room temperature to 6 GPa at 500 K. Studies on CoCrFeNi [33] and CoCrFeNiMn [34] HEAs show that at the short chemical range order of Cr at low temperature, the electronic spin-flip and magnetovolume effects lead to the largest lattice distortion effect of the Cr element. [PERSON] et al. [35] demonstrated that the lattice distortion in CoCrFeNi HEAs contributes to the solid solution strengthening of alloys. With increasing Al content, CoCrFeNiAl\({}_{x}\) HEAs changed from FCC, FCC+BCC phase to BCC phase [36; 37], and their plasticity degraded [14]. The component and crystal structures of paramagnetic CoCrFeNiAl\({}_{x}\) alloys [37] have the most significant influence on the single and polycrystal elastic parameters, and the mechanical properties of equimolar CoCrFeNiAl are better than a single-phase structure. Although Co-Cr-Fe-Ni HEAs are among the most widely studied high-entropy alloys, there is little information on the influence of composition on their structural and mechanical properties. [PERSON] et al. [38] demonstrated that certain components of alloys significantly affected their properties--that is, Co affects the lattice parameter, Cr affects the enthalpy of mixing, Fe affects the bulk modulus, Co affects the shear modulus, and Cr affects the Pugh ratio (\(B/G\)). [PERSON] et al.