Effects of nano-h-BN and Ag-coated Cu on the microstructure and friction-reduction properties of self-lubricating composite coatings

High-strength steel (42CrMo) is frequently used to manufacture components under high load and high friction conditions. To improve the surface tribological properties, nickel-based alloy coatings with Ag(Cu)/nanoNi/h-BN nanosheets were prepared on the surface of 42CrMo steel by laser cladding technique. The effects of Ag(Cu) and nanoNi/h-BN on the microstructure evolution, hardness and friction-reduction properties of the cladding layer were discussed. The results show that the coating microstructure changes significantly. The addition of micron Ag(Cu) and nanoscale Ni/h-BN increased the nucleation rate of the melting pool, and the columnar dendritic crystals were transformed into fine cells. The addition of nanoparticles enabled the coating to obtain a higher microhardness of 575.4HV0.2, which is about 1.4 times of the substrate. The mechanical properties of the coating were improved, and the friction coefficient and wear rate were significantly reduced, with good friction-reduction property. The wear mechanism mainly consists of a composite wear of slight adhesive wear, abrasive wear and oxidation wear.