In-situ NbC reinforced Fe-based coating by laser cladding: Simulation and experiment

In-situ NbC reinforced Fe-based coating was fabricated on the middle carbon steel surface by laser cladding with the mixture of niobium and boron carbide powder, aiming at revealing the mechanism of in-situ synthesis and improving the hardness and wear performance. The possibility and mechanism of in-situ synthesis were explored for the first time by combining simulation with experiment. The phase composition, microstructure characteristics and evolution mechanisms of the coatings were investigated by X-ray diffraction and scanning electron microscopy. The strengthening mechanism of hard phases on hardness and wear performance of coating were analyzed in detail. The results show that Marangoni convection promoted the melting of particles and improved the uniformity of solute atoms. The composite coating is mainly comprised of reinforced phases (NbC, Fe2B, B4C) and the matrix ([Fe-Cr] solid solution). The dispersive NbC particles (average diameter similar to 1.03 mu m) in-situ formed at the grain boundary achieved the dispersion and fine-grained strengthening effect. The hardness of the composite coating is 866.36 HV0.5, which is 3.95 times and 4.16 times that of the substrate and Fe-based coatings. The volume loss of composite coating reduced more than five times as compared to the substrate and Fe-based coating, and the wear mechanism changed from abrasive wear to adhesive wear due to the addition of Nb and B4C powders.