Microstructure And Properties Of Nano-particle Reinforced Ni-based Composite Coatings

With the rapid development of modern engineering, the surface of the material is required high overall performance.Cladding material has been gradually developed from the initial selection of self-fluxing alloy system to a composite material system. Its enhanced phase mainly involves hard ceramic particles. The internal defects of these micron hard phase and large difference in thermal property between the matrix and the substrate are easily lead to cracks, holes and other defects in composite coating with laser cladding process.because of special structure and size effect, nano-materials not only has excellent mechanical properties, but also with less defects of interior microstructure, Therefore, the generation of the interfacial stress concentration can been alleviated to some extent, and then obtains high-quality metallurgical bond coating.In the present study, Ni-based composite coatings with different nano-TiC/C and nano-TiN additions were prepared by laser cladding on the surface of38CrMoAl steel substrate, respectively. The influence of nano-TiC/C and nano-TiN on the microstructure and properties of the coatings was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness tester, and friction wear testing machine.Nano-TiC/C is a kind of composite powder material of a core-shell structure. The presence of the C coating layer can avoid the reunite between the nano-particles. TiC phase in the core can significantly improve the friction and wear properties of the composite coatings. Experiments showed that the Ni-based composite coatings with different nano-TiC/C additions mainly consist of γ-Ni, Ni3B, and M23C6phases. However, there are distinctive differences in content, size, and morphology of the constituent phases. With the increase of the nano-TiC/C additions, the microstructure is refined, the content of the primary y-Ni dendrite is increased, and its growth morphology changes from columnar dendrite to equiaxed dendrite. However, when the nano-TiC/C addition is increased to5.0wt.%, the size of the primary y-Ni dendrite begins to increase slightly, and its growth morphology is changed into columnar dendrite again as the nano-TiC/C addition is further increased to15.0wt.%. At the same time, the constituent phases of the eutectic change from y-Ni+Ni3B to y-Ni+M23C6. The content, morphology, and distribute of TiC in the coatings are mainly related to the dissolution and movement of nano-TiC/C in high temperature molten pool. With the increase of the nano-TiC/C additions, the hardness of the coatings is gradually increased, while the anti-friction property and the wear resistance present a trend of first increasing and then decreasing, i.e., the both reach the highest at1.5wt.%and5.0wt.%nano-TiC/C additions, respectively. Nano-TiN has advantages of high hardness and corrosion resistance. As a reinforcing phase, nano-TiN can significantly improve the friction and wear properties of the composite coatings. Experiments showed that the Ni-based composite coatings with different nano-TiN additions mainly consist of y-Ni, Ni3B, TiN, and M23C6phases. However, with the increase of the nano-TiN additions, the content of the TiN is increased, the content of the primary y-Ni dendrite is increased, and its growth morphology changes from columnar dendrite to equiaxed dendrite. However, when the nano-TiN addition is exceed to5.0wt.%, the size of the primary y-Ni dendrite begins to reduce slightly, and its growth morphology is changed into columnar dendrite again as the nano-TiN addition. With the increase of the nano-TiN additions, the hardness of the coatings is gradually reduced, while the anti-friction property and the wear resistance present a trend of first increasing and then decreasing, i.e., the both reach the highest at15wt.%and5wt.%nano-TiN additions, respectively.