Effects of the proportions of carbon on the microstructure and properties of NbC-reinforced Ni-WC composite coatings by laser cladding in-situ synthesis

Abstract

Laser cladding was utilized to prepare NbC carbide-enhanced Ni-WC composite coatings in the work. First-principle calculations and tests were conducted to study the effects of different proportions of carbon on the characteristics and organization of in-situ synthesized NbC-enhanced coatings. Firstly, differences in coating phases and microstructures were analyzed under different proportions of carbon according to the experiment. NbC with lower Gibbs free energy was the first to precipitate, and other compounds were non-uniformly nucleated around NbC in terms of thermodynamic calculation results. The higher the proportion of carbon, the finer the grain structure. The tests of hardness and friction wear showed that the higher the proportion of carbon, the better the hardness and wear resistance of the coating. The difference in grain morphology was the main reason for the difference in coating performance. Secondly, the first-principles calculation was used to model NbCx. The elastic modulus, mechanical properties, anisotropy, and electronic properties of carbides were calculated to explore the effects of carbon vacancies on the properties of NbC. The mechanical properties of carbides decreased with increased carbon vacancies, accompanied by increased anisotropy and weakened covalence. The results provide a theoretical foundation for understanding the effects of the proportions of carbon on nickel-based composite coatings prepared by laser cladding.