Microstructure and Properties of Laser Cladding (Ni60+NbC)+h-BN@Cu Coatings

The performance of laser cladding Ni-based NbC coatings was improved by adding copper-clad hexagonal boron nitride (h-BN@Cu) powder. Nickel-based Niobium carbide composite powder with different mass fractions of copper coated with hexagonal boron nitride was deposited on the surface of 45 steel matrix by laser cladding technology. A scanning electron microscopy (SEM) was used to analyze the microstructure and hard phase distribution of the coating; The phase composition was analyzed with an energy dispersive spectroscopy (EDS); The phase in the coating was characterized by X-ray diffraction (XRD); The microhardness of the cladding layer was measured with a microhardness tester; The wear resistance of the cladding layer was tested with a Bruker UMT-2 friction testing machine, and a white light interference module was used. The three-dimensional topography of the wear scar was measured, and the wear volume was calculated. The results showed that the main phase in the cladding layer was Ni-Cr-Fe, and other phases such as FeNi3, CrB, M7C3, NbC, M23C6 and Cr2Nb existed. The study found that when h-BN@Cu was not added, the cladding layer was mainly composed of Ni-Cr-Fe, FeNi3, CrB, M7C3, NbC, M23C6 and other phases, and the shape of NbC particles was mainly irregular polygons. After the addition of h-BN@Cu, the unmelted h-BN phase in the cladding layer increased, and the NbC morphology changed to a cross-like and petal-like structure, and the other phase compositions did not change significantly. This was due to the coating effect of Cu powder, which prevented the melting of part of h-BN, while with the increase of h-BN@Cu content, the laser absorption efficiency during the cladding process was improved, so that the molten pool absorbed more energy and promoted NbC particles disintegrate and re-grow. And after the addition of h-BN@Cu, the reflectivity of the laser was reduced and the dilution rate was increased. Excessive addition of h-BN@Cu would cause pores in the cladding layer and reduce the performance of the cladding layer. This was because after the addition of h-BN@Cu, the molten pool absorbed too much energy, which leaded to the decomposition of part of h-BN into B and N. N and O in the surrounding environment generated NO, which was then melted under the action of Marangoni flow. Pore defects were formed in the middle and lower part of the cladding layer, which affected the performance of the cladding layer. When the h-BN@Cu content gradually increased, the wear resistance of the cladding layer first increased and then decreased due to the good lubricating properties of Cu and h-BN. When the h-BN@Cu content was 10%, the friction coefficient of the cladding layer was 0.4, the wear scar width was 0.406 mm, and the wear resistance was the best. Compared with the Ni60/NbC cladding layer without h-BN@Cu, the average hardness of the Ni60/NbC cladding layer with h-BN@Cu is slightly decreased, but the hard phase distribution of the cladding layer is more uniform, and the hardness is still 3.1 times that of the 45 steel matrix. The friction coefficient is reduced by about 27%, and the wear scar width is reduced by about 21%. The research results provide a reference for the preparation of nickel-based composite coatings with excellent performance. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.