Microstructure and properties of BN-reinforced Ni60–Cr₃C₂ coatings fabricated by ultra-high-speed laser cladding

Taking Cr₃C₂ powder, h-BN powder and Ni60 powder as raw materials, BN-reinforced Ni60–Cr₃C₂ composite coatings were fabricated on the surface of quenched and tempered 40Cr cylindrical bars via ultra-high-speed laser cladding technology. The effects of BN on the microstructure and properties of Ni60–Cr₃C₂ coatings were systematically investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), Vickers microhardness test, friction and wear test, and electrochemical measurement. The results show that the Ni60–Cr₃C₂ coating is mainly composed of Cr₃Ni₂, Cr_1.12Ni_2.88, Cr₇C₃ and Fe₃C phases. After the addition of BN, in-situ synthesized Fe₂B, Cr₂N and Cr₂B₃ phases are formed in the coating. BN can promote the decomposition of residual Cr₇C₃ and the formation of Cr-rich dendritic networks within the coating. The microstructure uniformity and wear resistance of the BN-reinforced Ni60–Cr₃C₂ coating are significantly improved. Compared with the pure Ni60–Cr₃C₂ coating, its volume wear loss is reduced by 53.3%. In addition, the BN-reinforced coating exhibits an enhanced corrosion resistance, with a corrosion current density of 1.28×10⁻⁶ A·cm⁻², which is 81.0% lower than that of the Ni60–Cr₃C₂ coating. Its charge transfer resistance reaches 5562 Ω·cm², 2.2 times that of the original Ni60–Cr₃C₂ coating.