Application of Laser Cladding Technology in the Performance of Metro Wheels

The importance of wheels in the operation safety of metro vehicles

Due to the high efficiency and capacity of railway transportation, railway transportation has been established as one of the most important alternatives to reduce traffic congestion, especially in urban areas.

Although there has been no major or serious safety accident, the development of industry and technological progress have really improved the importance of safe train operation.

Wheel is one of the important components of metro vehicles. The characteristics of subway lines are more complex than high-speed trains. Frequent braking and acceleration can easily damage the wheels.

Common types of wheel damage include rim wear, tread scratch, tread wear, tread peeling and rim peeling. In addition, in the process of wheel maintenance, the relative movement between the wheel and the rail may cause the wear of the tire surface.It is very important to study the wheel sliding friction performance to ensure train safety.

Laser cladding technology for studying wheel sliding friction

Laser cladding technology deposits the surface layer of metal alloy on the substrate, which has many potential applications in automobile industry, the repair of high value-added parts, and has a strong ability to resist wear and rolling contact fatigue cracks.

Laser cladding technology strengthens the material and makes the surface of the substrate obtain superior quality. Most researchers believe that laser cladding technology and laser welding technology  can use various alloy powders to produce alloy coatings with wear resistance, friction reduction, corrosion resistance, fatigue resistance and oxidation resistance.

The selection of appropriate alloy powder is very important for laser  technology. Iron-based and nickel-based powders are often used in track and wheel structures. However, the two powders are different in composition, function and characteristics.

Analysis of dry sliding friction and wear properties of Ni and Fe alloys in the repair of metro wheel hub

It is understood that researchers from East China Jiaotong University, such as Xiao Qian, Zhang Bo and Yang Wenbin, have compared the performance of Ni-based and Fe-based alloy coatings in the repair of subway wheels. The ER9 material of railway wheels is coated with Ni-based and Fe-based alloys by laser melting technology, and the coating structure is dense, without defects, cracks or pores.

The microstructure, interface elements and phase types of the coating were studied by energy dispersive spectrometer (EDS), scanning electron microscope (SEM), 3D optical morphology and X-ray diffraction (XRD).

MFT-EC4000 reciprocating electrochemical wear and friction tester and Vickers microhardness tester were used to test the mechanical properties of the coating. Experiment selection has γ Ni-based coatings with (Ni, Fe), Cr23C6 and Cr7C3 phases and γ- Fe-based coating of Fe, (Fe-Cr-Ni) and (Fe, Ni) solid solution phase.

In Ni-based alloys, chromium deposition enhances the bonding between atoms and contributes to solution strengthening. In addition, the existence of hard carbide phase and the solid solution in the cladding layer structure increase the compressive strength and tensile strength of the material.

When adhesive wear is the main wear mechanism, the Ni-based coating undergoes more serious oxidation at the end of wear and friction tests. The hardness of Fe-based coating is 715 HV0.7, 2.86 times that of the base material. The maximum hardness of Ni-based coating is 268.4 HV0.7.

In addition, the friction coefficient of Ni-based coating is lower than that of Fe-based coating. In terms of wear and friction, the durability of Ni-based coating is about four times that of Fe-based coating.

Due to the existence of solid solution phase, the Fe-based coating shows solid solution strengthening. Local quenching occurs due to preheating of molten coating, which increases the hardness and wear resistance of the structure.

The function of Ni-based coating at high temperature is expected, and its hardness and friction quality are also low. However, the economic benefits of Ni-based alloys are poor.

This research shows that laser cladding technology can improve the hardness and wear resistance of wheels. In addition, the research shows that when the alloy coating is the same as the underlying material, the alloy powder can bring more significant performance improvement.

Due to the best wear relationship between rail and wheel, as well as the high wear resistance and hardness of the coating, Fe-based coating is not suitable for wheel cladding.

About HGSTAR: HGSTAR is is a sub-brand of HGTECH.HGTECH the pioneer and leader of laser industrial application in China, and the authoritative provider of global laser processing solutions. We have comprehensively arranged laser intelligent machine, measurement and automation production lines, and smart factory construction to provide overall solutions for intelligent manufacturing.

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