| Heavy-haul transportation is drawing unprecedented attention all over the world as it greatly improves the ability of transporting goods due to its operating model of large axle load and high density. With the development of heavy-haul freight in our country, the wear of wheel/rail has been paid great attention and the reduction of wheel/rail wear and damage is a key problem to solve after the use of big axle load locomotives in the upgrade lines especially. More and more scholars who study wheel/rail focus on the development of laser surface processing and it has a certain practical significance for extending the life time of heavy-haul rail by improving the wear properties of wheel/rail material owing to the laser surface treatment.In present paper, field investigation and collecting damaged rail specimens are done in Datong-Qinhuangdao heavy-haul railway and the damage of heavy-haul railway is studied through macroscopic and microscopic test and analysis. Then, laser quenching and laser cladding, are done on the surface of wheel/rail material by CO2multimode laser and functional layer is obtained. Furthermore, microscopic analysis such as the structure, the hardness and the phase are made for the functional layer. The wear and damage properties of treated heavy-haul wheel/rail are studied using a MMS-2A rolling wear test apparatus and the wear resistance of wheel/rail is investigated with an increasing axle load. The microstructure, wear properties and surface damage behavior of wheel/rail are investigated in detail using various examinations such as hardness tester, scanning electron microscope and X-ray diffraction. The main conclusions are as follows:(1) The wear and surface damage of heavy-haul rail in the field is severe and stripping damage is dominating. For the rail, fatigue cracks are concentrated on the rail corner and the residual stresses present compressive stress state. Furthermore, there is severe plastic deformation on the rail corner and the damage behavior of heavy-haul railway is abrasion and stripping damage.(2) The surface hardness of wheel/rail materials is increased significantly by laser quenching treatment. The wear resistance of wheel/rail that treated with laser is improved obviously and the wear decrease rates of wheel and rail are about44.02%and13.6%, respectively. The wear rate of wheel or rail specimen is induced as single wheel or rail specimen treated with laser transformation hardening. However, the wear of other friction pair without laser transformation hardening is aggravated. The deformation resistance of wheel/rail material is effectively improved as wheel and rail specimens treated with laser quenching and the damage is slight. For rail with laser quenching treatment, slight fatigue wear is dominating. For wheel with laser quenching treatment, the adhesive and fatigue wear are exist, and fatigue wear is dominated.(3) Laser coating, which has a good metallurgical bonding with substrate, is obtained by laser cladding treatment on the surface of wheel/rail material. The coating is consisted of dendrite (y-Co) and eutectic (Cr23C6+γ-Co). The hardness and wear resistance of wheel/rail material are improved obviously than that of substrate and it would significantly reduce the wear rate of other friction pair without laser cladding. The wear rate of wheel/rail would decrease markedly when wheel and rail specimens are treated using laser cladding and the reduction of wear rate of wheel/rail material are78.18%and80.43%, respectively. With an increasing axle load, the wear rate of wheel/rail material increases. For treated heavy-haul wheel/rail material, slight adhesion wear is dominating damage mechanism. The fatigue resistance of laser cladding coatings is improved significantly.(4) The wear and damage properties of heavy-haul wheel/rail material are well improved by laser cladding compared to the laser quenching treatment and it is one of effectively methods to alleviate the wear and damage of wheel/rail material in heavy-haul condition. |
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