As an efficient and high-capacity mode of transportation, the subway has become one of the most important alternatives to reduce traffic congestion, especially in urban areas. Wheels are one of the important parts of subway vehicles. The characteristics of subway lines are more complex than high-speed trains, and frequent braking and acceleration can easily damage the wheels. Common types of wheel damage include rim wear, tread scuffs, tread wear, tread spalling, and rim peeling. In addition, the relative movement between the wheels and the rails during wheel repairs may cause wear on the tire treads. Therefore, it is very important to study the sliding friction performance of wheels to ensure the safety of subway.
Laser cladding technology deposits a surface layer of metal alloys on the substrate, which has many potential applications in the repair of high value-added parts and possesses strong resistance to wear and rolling contact fatigue cracks. Laser cladding technology strengthens the material and enables the substrate surface to obtain superior quality. Most researchers believe that laser cladding technology can produce alloy coatings with wear resistance, friction reduction, corrosion resistance, fatigue resistance and oxidation resistance using various alloy powders.The selection of suitable alloy powder is crucial for laser cladding technology. Iron-based and nickel-based powders are often used in track and wheel construction. However, the two powders differ in composition, function and properties. The following is the dry sliding friction and wear performance analysis of Ni and Fe alloys in the repair of subway hubs
It is understood that the ER9 material of railway wheels is coated with Ni-based and Fe-based alloys by laser cladding technology, and the obtained coating has a dense structure, no defects, no cracks or pores.
Schematic diagram of the friction test.
The researchers used energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), 3D optical topography, and X-ray diffractometer (XRD) to study the coating’s microstructural morphology, interfacial elements, and phase types.
In Ni-based alloys, chromium deposition enhances interatomic bonding and contributes to solid solution strengthening. Furthermore, the presence of hard carbide phases and solid solutions in the cladding structure increase the compressive and tensile strength of the material. When adhesive wear was the dominant wear mechanism, the Ni-based coatings experienced more severe oxidation at the end of the wear and friction tests. The hardness of the Fe-based coating is 715 HV0.7, which is 2.86 times that of the base material. The maximum hardness of the Ni-based coating is 268.4 HV0.7. In addition, the friction coefficient of Ni-based coatings is lower than that of Fe-based coatings. In terms of wear and friction, Ni-based coatings are approximately four times more durable than Fe-based coatings. Fe-based coatings exhibit solid solution strengthening due to the existence of the solid solution phase. Local quenching occurs due to preheating of the molten coating, which increases the hardness and wear resistance of the structure. Ni-based coatings function as expected at high temperatures, and their hardness and friction qualities are also on the low side. However, Ni-based alloys are less economical.
This study shows that laser cladding technology can improve the hardness and wear resistance of wheels. In addition, studies have shown that alloy powders can bring more significant performance improvements when the alloy coating is the same as the underlying material. Fe-based coatings are not suitable for wheel cladding due to the optimal wear relationship between rail and wheel and the high wear resistance and hardness of the coating.
Jinan SENFENG Laser Technology Co., Ltd. dedicated to the industrial application and promotion of laser cladding technology. The company has established a laser cladding technology research and development center, production and processing center. Based on the application requirements of a large number of domestic and foreign customers, customized development process and core equipment, with the ability to provide customers with industrial application technical services, including powder material selection, equipment configuration, process control, technical support and upgrade services. If you want to know more about laser cladding machine, please contact SENFENG.
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