| Laser cladding technology develops rapidly in recent years, it is used more widely in the aerospace, automobile, machinery, chemical industry, and generate vast economic and social benefits. Laser cladding is an advanced surface modification technology to prepare cladding layer on the substrate surface which has metallurgical bonding, wear, corrosion, oxidation and other excellent performance.Silicides of transition metal W(e.g. W5Si3 and WSi2) have high melting point, high temperature strength and low-temperature plastic deformation potential. But as an intermetallic compound, W silicide high temperature brittleness, its industrial applicationsas friction and wear parts are severely limited. There are many methods to improvetoughness of metal silicide coating. The method use of high ductility Ni-based coating has remarkable results, due to its high plasticity, toughness, high strength combined with silicide. Nb silicides have the potential to be used as high temperature structural metal, and its inherent stiffness and abnormal high hardness- temperature relationship bring aboutoutstanding ability of abrasive and adhesive wear resistance.In this paper, laser cladding technique was adopted to prepare Ni-W-Si composite coatings on the surface of 304 stainless steel and 45 steal, and Ni-Nb-Si coatings on T2 copper. Through several experiments to optimize the parameters, single-channel claddinglayer with higher quality, fewer defects were formed ultimately. A larger area of the cladding was prepared by multi-track lap with optimal parameters. The microstructure, the composition and distribution phase of the cladding layer was observed and analysed through by using optical microscopy, scanning electron microscopy, Energy Dispersive Spectroscopy and X-ray diffraction.The coating’s microstructure of different Ni-W-Si components are closer to each other by laser cladding on the surface of 304 stainless steel substrate. Plenty of petal-like or cell-like W5Si3, Cr Si2and(Fe, Ni) composite phase are precipitated in the coatings, and the amount of these phase increased with the increase of W, Si element contents in the powder. The coating hardness and wear resistance are improved due to these phases. When on the surface of 45 steel substrate, the microstructure of coatings are mainly consists of columnar crystals(Fe-Ni solid solution) and intergranular silicide(W5Si3+ WSi2) components. The higher ratio of W element in powder, the more unmelted W particles residue in the coating after laser cladding. During the process of solidification, the new phases adhere to the W particles and gradually completely wrapped, the final presentation having a sandwich structure the petals or cellular structure. The coating’s microstructure of different Ni-Nb-Sicomponents are closer to each other by laser cladding on the surface of T2 copper substrate. The coatings are consists of dendritic or columnar crystals Ni2 Si, Nb Si2 and Nb5Si3composite phase, and(Ni, Cu) solid solution dendrites constitution. With the increase ofNb content in the coatings, more dense dendrite, columnar crystals gradually reduced.The microhardness testing and tribological test results show that Ni-W-Si laser cladding coating with good friction and wear resistance, wear mechanism is mainly abrasive wear; high resilient W5Si3 and supersaturated solid solution of Ni-based distributed in the coatings, greatly improved the microhardness of coating to HV1040, about four times of the stainless steel substrate and the coating of dry sliding friction and wear resistance is significantly enhanced. Ni-Nb-Si-coated microhardness and wear resistance have been significantly improved compared to the base 45 steel induced by carbide phase Nb Si2, Nb5Si3, supersaturated solid solution of Ni-based coating tissue. With the increase of Nb content, the hardness of the coating has been significantly improved, the wear weight loss also decreases. Friction and wear mechanism is mainly abrasive wear coating along trace adhesive wear and dry sliding friction. The wear resistance at room temperature has been significantly enhanced. |
PDF Full Text Request