## 3 Results and Discussions
### Microstructure, Phase Formation, and Phase Composition
Increasing the content of B from 0.5 to 1.5 can decrease the intensity of the diffraction peak corresponding to the FCC solid solution (211) and the shift of the diffraction peak to the higher angle. This phenomenon was due to the increasing B content, which can increase the number of soluble atoms of B in the crystal structure. However, the B atom was greatly different in terms of size, from the other atoms, thereby increasing lattice distortion. Thus, the diffuse reflection effect was strong, and the intensity of the diffraction peak was reduced. Moreover, the radius of the B atom was smaller than that of the other atoms, and its displacement ability to other elements was strong. With increasing displacement of the B atom to the other atoms in the crystal structure, the lattice constant decreased, thereby shifting the diffraction peak to the higher angle. SEM images of the microstructures of the laser-clad FeCoCrNiB\({}_{x}\) HEA coatings with three different B contents are shown in Figure 5. The coatings exhibited a typical dendritic and interdendritic structure, and the microstructure was refined with the increase of B content. XRD analysis and the microstructure of FeCoCrNiB\({}_{0.5}\) coating in Figure 5a shows that the dendrites were identified to belong to the primary FCC solid solution and interdendrites were identified to belong to the FCC solid solution phase and a small quantity of the M\({}_{2}\)B phase. According to Figure 5a-c, the volume fraction of the M\({}_{2}\)B phase increased and dendrites decreased gradually with the increase of the molar ratio of B content. The FeCoCrNiB\({}_{1.0}\) coating was composed of the eutectic structure of the FCC solid solution and the M\({}_{2}\)B phase. When the molar ratio of B content increased from 1.0 to 1.5, the coating was composed of the eutectics of willow-like primary M\({}_{2}\)B phase, M\({}_{2}\)B phase, and FCC solid solution phase, and the microstructure tended to blocky. Figure 4: X-ray diffraction patterns of the laser-clad FeCoCrNiB\({}_{x}\) (\(x\) = 0.5, 1.0, and 1.5, respectively) high-entropy alloy (HEA) coatings. (**a**) 20 from 20\({}^{\circ}\) to 100\({}^{\circ}\), (**b**) 20 from 64.5\({}^{\circ}\) to 66.5\({}^{\circ}\). For mapping the compositional distribution, EDS map analysis of the alloy elements are presented in Figure 6. The qualitative segregation characteristics can be visualized, and the EDS results of FeCoCrNiBx coatings are shown in Table 3. According to Figure 6a-f, when the molar ratio of B content was 0.5, Fe, Co, and Ni were increased in terms of the amount in the gray dendritic regions, while Cr and B were reduced in the dendritic structure. XRD analysis showed that the main gray dendrite structure was the FCC solid solution. The Fe content in the white interendritic structure was the highest, followed by Cr and B, thereby indicating slight component segregation. A small number of borides was also observed in the structure. According to the XRD results, the gray dendritic and white interendritic structures were the FCC solid solution. Increasing the molar ratio of B content to 1.0 resulted in a complex coating structure. The EDS results in Figure 6g-l show that the contents of Cr and B in the dendritic structure were the lowest, whereas those of Fe, Co, and Ni were higher. The XRD analysis showed that the gray dendritic structure was composed of the FCC solid solution, whereas the white interendritic structure was composed of the FCC solid solution and a small amount of the M2B phase. As shown by the EDS results in Figure 6m-r, when the molar ratio of B content was increased to 1.5, large amounts of Fe, Co, and Ni were enriched in the gray dendritic structure. The XRD results showed that the gray dendritic structure was composed of the FCC solid solution, whereas the white interendritic structure was composed of the eutectic structure of the FCC solid solution and the M2B phase.