Study On Friction And Wear Properties Of Heavy-Haul Wheel/Rail Materials For Laser Cladding

Heavy-haul railway as an important direction of development is unprecedented attention all over the world. However, with the development of heavy-haul railway, some key technical problems are appearing, among which the most important is the wheel/rail wear. Wheel/rail wear is the result of a variety of factors. Furthermore, the hardness matching of wheel/rail materials plays an important role. Therefore, experimental research on heavy-haul wheel/rail materials for laser cladding is important for improving material properties to reduce the wheel/rail wear and ensuring the safety of heavy-haul rail transport.Laser cladding of Co-based alloy on heavy-haul wheel and rail materials were carried out by CO2laser. The microstructure and micro-hardness of laser cladding layers were analyzed in detail. According to the Hertz contact theory, the friction and wear properties of wheel/rail before and after laser cladding Co alloy coatings were investigated using MMS-2A rolling wear machine under25T,32T, and35T axle load conditions. Organizational structure, wear, and friction coefficient and wear scar damage morphology of heavy-haul wheel/rail specimens were explored with the help of optical microscopy (OM), Vickers hardness tester (MVK-H21), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Main conclusions are drawn as follows.1. High quality cladding coating with the thickness of about1mm can be obtained. Laser cladding layer has an excellent metallurgical bonding with the substrate and no defects of pores and cracks. The cladding layer mainly consists of these phases of y-Co, Cr23C6and so on. There are some crystallization morphologies, such as planar, cellar, columnar and twin microstructure. The micro-hardness of cladding layer of wheel and rail specimens respectively increase43%,45%compared with wheel/rail materials without laser cladding.2. Friction and wear properties of Co coatings are obviously better than wheel/rail materials without laser cladding under25T axle load condition. The wear resistance of coatings is improved about4times than wheel/rail materials without laser cladding. Main wear mechanism of cladding coatings is abrasive wear. The wear mechanism of wheel/rail specimens without laser cladding is spalling damage and oxidation wear.3. The wear volume and friction coefficient of wheel/rail specimens before and after laser cladding increase with the increase of axle load. The wear mechanism of wheel/rail specimens with laser cladding change from abrasive wear to adhesion wear and spalling damage when the axle load increases from25T to35T. However, the wear mechanism of wheel/rail specimens without laser cladding change from adhesion wear to serious spalling damage and oxidation wear.