| Heavy-haul is a major trend of railway transportation. And it has characteristics of heavy axle load and high transportation capacity. With the development of heavy-haul technology, great contributions have been made for the modern society by heavy-haul. However, some problems which should be immediately solved turn up and the wear of the wheel and rail is one of the most important problems among them. Laser cladding is a kind of advanced surface treatment technology, which has been applied to the surface treatment of wheel and rail materials by many researchers. They used laser cladding surface treatment technology on the surface of rail/wheel material of heavy-haul to reduce the wear and damage. It can improve the safety of railway and reduce the costs of transportation.In this study, the material that used during laser cladding is Fe-based alloy powder and three mixture added different contents of lanthanum oxide. The three mixtures are mixed with 0.4%,1.2% and 2% lanthanum oxide and Fe-based alloy. Four kinds of rail/wheel specimens with laser cladding Fe-based alloy coatings are obtained after the laser cladding surface treatment using a multimode cross flow CO2 laser (TR-3000). The microstructure, the hardness and the phase of the laser cladding coatings are analyzed and tested by means of Vickers hardness instrument, optical microscopy X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The wear and rolling contact fatigue properties of laser cladding wheel/rail specimens are studied using a MMS-2A rolling-sliding wear testing apparatus.The main conclusions are as follows:(1) The cladding coating is uniform and compact and there is no crack and stomata. And it has two structures, dendrites and eutectic. Affected by the solidification conditions, the large crystal structure is observed in the binding region while cellular dendrite and dendrite is observed from the middle to the surface region. And (Fe, Ni) solid solution is formed by Fe and Ni and high-hardness carbide can be easily formed by Cr. After adding lanthanum oxide, lanthanum oxide gathers in the boundary of the grain by diffusion mechanism, which change the energy of boundary and structure of the grain and reduce the tension of grain boundary. Therefore, the driving force of grain growth reduce, which refine the grain. As a result, the organization become more uniform and eutectic structure refinement and dispersion increased significantly.(2) After laser cladding, the dendritic structure has good toughness and the eutectic network has high hardness. They form the special structure and make the cladding coating of specimens have high surface hardness and good toughness. The wear resistance of the Fe-based laser cladding wheel/rail specimens is improved obviously and the wear decrease rates of wheel and rail specimens are about 32% and 42%, respectively. Therefore, the surface damage of the specimens alleviates effectively and the deformation resistance and cracks resistance of wheel/rail specimens are improved. The wear mechanism of laser cladding wheel/rail is changed from dominated by slight fatigue wear to slight fatigue and adhesive wear.(3) After adding different content of lanthanum oxide, the lanthanum oxide gathers in the grain boundary, which prevents grain growing and strengthens the grain boundary. And then the grain slips easily. It is in favor of the stress relaxation of the micro cracks at the top of organization and the increase of the crack extension resistance. As a result, the wear resistance of the laser cladding wheel/rail specimens have been further improved. After adding 1.2% lanthanum oxide, anti-resistant of the cladding wheel/rail specimens is better than others and the wear decrease rates are about 46% and76%, respectively. Meanwhile the surface damage of the specimens effectively alleviates and the deformation resistance and cracks resistance of wheel/rail specimens are improved.(4) Under the condition of oil lubrication, the surface damage of the laser cladding wheel/rail specimens are slight and the performance of preventing fatigue spalling is improved significantly. After adding lanthanum oxide, grain boundary is purified and grain size is refined which improve microstructure of the cladding coating. Therefore the grains don’t fracture easily and the toughness of materials is enhanced. In addition eutectic structure was finer and the dispersion degree increased. As a result the damage properties of the laser classing wheel/rail specimens are farther improved and the rolling contact fatigue performance of laser cladding specimens with 1.2% lanthanum oxide is better than others. |
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