In order to improve the wear resistance and corrosion resistance of agricultural soil-engaging tools, FeCoNiCrAl composite coatings with different contents of Nb and B4C were successfully prepared on the surface of 65Mn steel by laser cladding technology. The effects of Nb and B4C addition on the phase composition, microstructure, microhardness, friction and wear properties and corrosion resistance of the coatings were systematically studied. XRD analysis shows that the 0 % Nb-B4C coating is mainly composed of FCC, BCC and B2 phases. After the addition of Nb-B4C, hard reinforcements such as NbC, NbB2 and CrB2 were formed in situ. Microstructure analysis shows that with the increase of Nb and B4C content, the microstructure of the coating is gradually refined, and the Nb particles in the 15 % and 20 % Nb-B4C coatings fail to decompose completely in the limited life of the molten pool. With the increase of Nb-B4C content, the average microhardness of the coating also increased from 531.1 HV0.2 to 651.3 HV0.2, which effectively improved the ability of the coating to resist plastic deformation. The friction coefficients of B4C composite coatings with different Nb contents were 0.54,0.54,0.42,0.47 and 0.47, respectively. The 10 % Nb-B4C coating has the lowest average friction coefficient.In addition, the wear rate also decreased significantly. The wear rate of 15 % Nb-B4C coating was the lowest, and the wear mechanism was mainly abrasive wear and oxidation wear. XPS analysis showed that elements such as Fe, Co, Ni, Cr, Al and Nb participated in the oxidation reaction during the friction process, forming friction oxidation products such as Fe2O3, CoO, NiO, Cr2O3, Al2O3 and Nb2O5. The electrochemical test results show that the 10 % Nb-B4C coating has the lowest self-corrosion current and the highest self-corrosion potential .It shows the largest electrochemical impedance arc radius, indicating that the surface protective film is more stable and the corrosion medium shielding ability is stronger. However, excessive Nb-B4C will lead to the increase of residual Nb particles, phase interface and local composition segregation, promote corrosion, and weaken the microstructure uniformity and corrosion resistance stability of the coating. These results show that the addition of appropriate amount of Nb and B4C can optimize the microstructure of the coating and improve the mechanical, wear and corrosion resistance of the coating.
 

laser cladding ; high entropy alloy coating ; in-situ reaction ; friction and wear ; corrosion