## 3 Results and Discussions
### Microhardness and Wear Properties  
The Vickers micro-hardness of the different B mole HEAs was measured from the substrate to the metallurgical bonding surface and then the cladding layer. Each cross section was tested for \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**M\({}_{2}\)B** & **Fe\({}_{2}\)B** & **Co\({}_{2}\)B** & **Cr\({}_{2}\)B** & **Ni\({}_{2}\)B** \\ \hline \(\Delta H_{mix}\) (KJ/mol) & 30 & 28 & 34 & 27 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Enthalpies of binary borides that might be formed in the alloy. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Coating Type** & **Zone** & **Fe** & **Co** & **Cr** & **Ni** & **B** \\ \hline \multirow{3}{*}{FeCoCrNiB\({}_{0.5}\)} & Nominal & 22 & 22 & 22 & 12 \\  & FCC & 26 & 24 & 19 & 21 & 10 \\  & M\({}_{2}\)B & 27 & 16 & 30 & 11 & 16 \\ \hline \multirow{3}{*}{FeCoCrNiB\({}_{1.0}\)} & Nominal & 20 & 20 & 20 & 20 \\  & FCC & 22 & 19 & 10 & 24 & 25 \\  & M\({}_{2}\)B & 22 & 18 & 22 & 8 & 30 \\ \hline \multirow{3}{*}{FeCoCrNiB\({}_{1.5}\)} & Nominal & 18 & 18 & 18 & 18 & 28 \\  & FCC & 21 & 18 & 11 & 35 & 15 \\ \cline{1-1}  & M\({}_{2}\)B & 22 & 9 & 26 & 6 & 37 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: EDS results of FeCoCrNiB\({}_{x}\) HEA coatings (in at.%). multi points from the substrate to the surface with an equal interval of 0.2 mm. Figure 7 shows the micro-hardness distribution ranging from the Q245R substrate to the surface of the coatings with various B additions. The average thickness of the coating was about 1.6 mm. It can be seen that the micro-hardness value of coating is much higher than that of the Q245R substrate material, and the maximum hardness value in three HEA coatings reached around 1025 HV0.2 when the molar ratio of B was 1.5. With the increase of the cladding height, no obviously regular change was found in the micro-hardness. Moreover, with the increase of the content of B, the hardness showed an increasing tendency. The reasons for this can be attributed to the grain refinement, Nano-precipitates, and increased crystal packing density in the coating due to the rapid cooling rate in the laser cladding process. Meanwhile, based on the changes in the contents of borides in all coatings with the addition of B, the gradual increase in hardness was related to the increase of the hard phase of boride. The lattice distortion was caused by the solid solution of elements in the matrix, which increased the resistance of the dislocation motion and made the gliding of the dislocation difficult, thus improving the strength and hardness of the alloy [32]. Since the gap formed by the solid solution of the HEA is small, it is generally believed that the form of the atomic solid solution belongs to the displacement solid solution, so the lattice distortion is mainly caused by the difference of atomic size. In order to quantitatively analyze the influence of atomic size on lattice distortion, the standard deviation of atomic size between dendrites was calculated as follows:  
\[a_{avg}=\sum\
olimits_{i=0}^{n}a_{i}c_{i} \tag{4}\]  
\[\mathrm{s}=\sqrt{\sum\
olimits_{i=0}^{n}\left(a_{i}-a_{avg}\right)^{2}c_{i}} \tag{5}\]  
where \(a_{i}\) is the atomic size, \(C_{i}\) refers to the molar fraction of each element, \(a_{avg}\) is the average atomic size, and \(\mathrm{s}\) is the standard deviation. The values of the atomic radius of Fe, Co, Cr, and Ni were very similar, which were 1.27, 1.26, 1.27, and 1.24, respectively. The standard deviation of Fe, Co, Cr, and Ni was very small. However, the value of the atomic radius of B was 0.95, which was much smaller than the other four principal components. As a result, the standard deviation was larger than FeCoCrNi. During the laser cladding process, a part of the B atom formed the hardness phase of borides with other metal atoms, and the other part of the B atom, as an interstitial atom, was dissolved in the FCC solid solution, i.e., dissolved in the matrix of the FCC solid solution.