## 1 Introduction  
Recently, high-entropy alloys (HEAs), which are defined as solid solution alloys that contain more than five principal elements in equal or near equal atomic percent (at.%) [1], have drawn rising interest from the materials science and engineering community since the first few papers on the subject were published in 2004 [2, 3]. Due to the high-entropy effect in thermodynamics and hysteresis diffusion effect in dynamics [4, 5], HEAs are usually composed of single solid solution phases, such as face-centered cubic (FCC) or body-centered cubic (BCC) structures, rather than complex intermetallic compounds. These particular structures with proper composition may contribute to the advantages of HEAs in such aspects as high mechanical strength, good ductility, high wear resistance, good resistance to oxidation and corrosion, etc. [6, 7, 8], providing more possible engineering applications in various fields. To date, the fabrication routes of HEAs are mainly focused on the HEA bulk ingots and the HEA coatings [9]. The HEA bulk ingots are usually fabricated by the arc melting technique [10] or the casting method [11]; however, these techniques have a limited size of ingot due to the formation of the simple solid solution phase in the HEAs, which requires a high cooling rate [9]. Furthermore, given that HEAs comprise multiple expensive elements in high content, it is costly to fabricate the HEA bulk ingots [12]. Thus, it is attractive to fabricate the HEA coatings with excellent properties on the cost-effective steel substrates. The alternative laser cladding deposition technique is used to fuse a designed alloy coating with about 1-5 mm thickness on the surface of a low cost iron substrate with a rapid solidification rate (10\({}^{4}\)-10\({}^{6}\)\({}^{\circ}\)C/s), which leads to significant effects of non-equilibrium solute trapping, avoiding component segregation and improving solubility of the coating [13; 14]. Therefore, significant efforts have been made to investigate the microstructure and mechanical properties of HEA coating by laser cladding [15; 16; 17; 18]. For example, [PERSON] et al. [15] investigated the influences of silicon (Si) (1.2 mol.%), manganese (Mn) (1.2 mol.%), and molybdenum (Mo) (2.8 mol.%) additions on the microstructure, properties, and coating quality of laser-clad FeCoNiCrCu high-entropy alloy coating and found that the FeCoNiCrCu coatings with or without Si, Mn, and Mo additions are both identified to be simple FCC solid solutions. Besides, the micro-hardness is much higher than that of the alloy prepared by the arc melting technique with the same composition. [PERSON] et al. [16] studied the microstructure of the laser cladding Al\({}_{x}\)FeCoNiCuCr coating, the effects of aluminum (Al) element content on the coating hardness, and the high-temperature micro-hardness of the coating. [PERSON] et al. [17] reported that the strengthening methods for HEA coating can be performed through substitutional solid solution strengthening, by the addition of elements with large atomic radii, such as Al and titanium (Ti), to induce high lattice distortion. However, [PERSON] et al. [18] indicated that the increased lattice strain and defects often lead to high brittleness and reduce the ductility and toughness of HEA coating. Recently, some studies [19; 20; 21; 22] reported the addition of small elements, such as boron (B) or carbon (C), can be used to improve the mechanical properties of HEAs. [PERSON] et al. [23] indicated that it is vital to improve the solid solubility of B and control the boride morphology through the addition of the B element in the fabrication of new HEAs. However, little research has been published on the effects of B content on the microstructure and wear properties of the laser alloyed HEA coatings. According to [PERSON]'s law [24], the wear resistance of materials is proportional to the hardness.