Fabrication of Ni-based composite coating reinforced with NbC particles by laser cladding

摘要

The in situ synthesized NbC particles reinforced Ni-based alloy composite coating has been successfully prepared on 1045 steel substrate by laser cladding a precursor mixture of Ni-based alloy, graphite and niobium powders. The microstructure, phase composition and wear property of the composite coating are investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and dry sliding wear test. The experiment results show that the coating is uniform, continuous and free of pores and cracks with excellent bonding between the coating and the substrate. The microstructure of the coating is mainly composed of y-Ni dendrite, a large amount of interdendritic eutectics of M_23(CB)_6, N_3B with y-Ni, M_23(CB)_6 type carbides and dispersed NbC particles. The growth mechanism of the NbC particles with cores is nucleation-growth and the un-melted niobium may act as the nucleation core for NbC, Compared to the pure Ni-based alloy coating, the hardness of the composite coating is increased about 36 %, giving a high average hardness of approximate HV_0.27_50. Moreover, the wear volume and wear rate of the composite coating are decreased about 50 % and 42 %, respectively. This is attributed to the presence of in situ synthesized NbC particles and their well distribution in the coating.