In recent years, the "sliding instead of rolling" approach has become a new trend in wind power bearings to achieve cost reduction and efficiency improvement. However, sliding bearings are prone to fatigue spalling, abrasive wear, corrosion, melting and other failure forms when carrying. Cladding tin bronze on 42CrMo sliding bearing materials can enhance surface tribological properties while reducing manufacturing costs. However, direct Cu-Fe bonding tends to generate porosity defects. This study proposes employing a transition layer to mitigate pore formation in laser-clad coatings, while employing orthogonal experimental design to optimize the copper alloy cladding process. The transition layer significantly suppresses porosity in the cladding layer. Building on this approach, the influence of the electromagnetic field on the microstructure and properties of the cladding layer was thoroughly investigated. By adopting the method of adding a transition layer and synchronously applying a composite electromagnetic field, the porosity of the copper alloy coating on 42CrMo bearing materials via laser cladding was reduced, thereby improving its friction and wear performance.
The substrate material was 42CrMo bearing steel with dimensions of 240 mm×25 mm×10 mm. The surface oxide layer was removed with an angle grinder and cleaned with ethanol. The cladding material employed was gas-atomized CuSn12Ni2 powder, which was dried at 110 ℃ before the experiment. Single-pass cladding layers were prepared at laser powers of 1 600, 1 800, and 2 000 W, scanning speeds of 2, 4, and 6 mm/s, and powder feed rates of 8, 10, and 12 g/min. Multi-pass overlapping samples were fabricated at the optimal parameters with a 20% overlap rate. The cross-sectional morphology of the cladding layers was examined with an optical microscope. The microstructure was characterized by scanning electron microscopy, while an energy-dispersive spectroscopy was employed to analyze the elemental composition and distribution. Phase identification was conducted via X-ray diffraction, and microhardness was measured with a Vickers hardness tester. Sliding wear tests were performed at room temperature with a friction-wear tester, and the coefficient of friction was recorded. The 3D wear profiles were analyzed with a laser confocal profilometer, and the wear rates were calculated.
The optimal cladding process is achieved at a laser power of 2 000 W, a scanning speed of 2 mm/s, and a powder feed rate of 8 g/min. By incorporating the Ni transition layer, the porosity of the cladding layer can be minimized to 0.1%, with no cracks observed at the interfacial bonding region. Without the transition layer, the primary phases in the cladding layer consist of α-Fe, (Fe, Ni), Fe-Cr, α-Cu, CuNi2Sn, Cu41Sn11, whereas with the transition layer, the main phases are α-Cu, CuNi2Sn, Cu41Sn11, exhibiting a distinct elemental transition at the interface and ensuring excellent bonding. Under the combined action of the transition layer and the electromagnetic field, the microstructure exhibits a dispersed network morphology. The optimized cladding layer exhibits a microhardness of 205.7HV0.3. Under dry friction and oil lubrication conditions, the friction coefficients are 0.367 and 0.118, with corresponding wear rates of 0.005×10-5 mm3·N-1·m-1 and 0.009×10-6 mm3·N-1·m-1. Wear rates of the sample with the transition layer are reduced by 68.8% and 35.7%, respectively, compared with those without the transition layer. The wear mechanism shifts from adhesive wear to abrasive wear. The addition of the transition layer reduces porosity caused by the decomposition of SnO2, significantly lowering the porosity of the optimized cladding layer. The transition layer suppresses Fe diffusion from the substrate into the cladding layer, eliminating Fe-rich phases in the surface layer. The surface layer primarily comprises a matrix phase and island-shaped precipitates. The Lorentz force generated by the electromagnetic field drives melt convection, promoting compositional homogenization. Under the synergistic effect of the transition layer and electromagnetic field, the microstructure achieves uniform distribution, leading to significant improvement in tribological performance.
Key words
42CrMo /
laser cladding /
copper alloy /
transition layer /
electromagnetic field /
porosity /
tribological properties
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Funding
National Natural Science Foundation of China (52035014); “Elite" Program of Zhejiang Province (2024SJCZX0040); Zhejiang Provincial High-Level Talents Special Support Program (2023R5210)
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