Study On Laser Cladding Inhibition Of Discharge Damage Under High-Speed Wheel/Rail Coupling Vibration Behavior

Under the trend of high-speed and heavy-load railway development,the contact vibration between the wheels and rails has intensified.Through the action of the traction loop current between wheels and rails,the surface of wheel/rail will inevitably have discharge corrosion damage,which will induce wheel/rail wear and premature failure.The laser cladding method is used to prepare a cladding layer that is applied to the surface of the wheel/rail with excellent anti-discharge corrosion performance and wear resistance,so as to inhabit the damage caused by pitting of the wheel/rail,which has important research significance.In this paper,the laser cladding method was used to successfully prepare cladding coating with a new nickel-based self-fusible alloy powder(Ni45 powder with 1%W,1%Mo and 2%Cu)and nano-cerium oxide on the surface of the wheel material,which can effectively reduce the wheel/rail discharge corrosion.Metallographic microscope(OM),scanning electron microscope(SEM),X-ray diffractometer(XRD),energy spectrum analyzer(EDS)were used to study the influence of different nano-cerium oxide content on the microstructure of the cladding layer and the influence of discharge corrosion on the morphology of the wheel/rail substrates and cladding layers;the thermal performance,anti-discharge corrosion performance,hardness and friction and wear of the cladding layer and the wheel/rail substrate were studied by using synchronous thermal analyzer,numerically controlled electric spark forming machine,microhardness tester and friction and wear testing machine.Based on the above test results,the cladding material composition was reasonably designed,and the wheel steel cladding layer was prepared using the optimal process parameters obtained by orthogonal tests.The influence of wheel steel cladding on the anti-discharge corrosion and friction and wear properties of wheel/rail materials was studied,and the feasibility of laser cladding to inhabit wheel/rail discharge corrosion was verified.The main conclusions drawn are as follows:(1)The mechanism of wheel/rail discharge corrosion was analyzed in the oil medium for electric spark:from the surface morphology of discharge corrosion,it can be seen that as the current increases,the discharge gap decreases,the surface pits become biger and deeper,and microcracks increase and deepen;the main components of the wheel/rail materials after discharge corrosion are Fe₃O₄ and martensite;the average hardness of the wheel/rail surface increases after discharge corrosion;the discharge corrosion rate of the wheel material(positive electrode)is always greater than that of the rail material(negative electrode).(2)On the surface of the wheel material,the laser cladding test was carried out with nickel-based self-fusible alloy powder(Ni45 powder with 1%W,1%Mo and 2%Cu)and different content of nano-cerium oxide.The optimal process parameters were obtained by orthogonal test:laser power 600W,laser scanning rate 200mm/min,and powder feeding rate20g/min.The structure of the wheel steel cladding added with nano-cerium oxide is fine and uniform.The structure of the wheel steel cladding layer is mainly dendritic and eutectic.The phase of the wheel steel cladding layer has not changed before and after adding nano-cerium oxide.The phase of the wheel steel cladding layer is mainly composed of(Fe,Ni)solid solution,M_xC_y carbide,and M_xB_yboride(M=Cr,Fe,W,Mo)and other hard phases.Compared with the wheel steel substrate,the microhardness of the wheel steel cladding layer after adding nano-cerium oxide is greatly improved.As the content of nano-cerium oxide increases,the average hardness of surface of the wheel steel cladding layer first increases and then decreases.Among them,the average hardness of the surface of the wheel steel cladding layer containing 1.5%nano-cerium oxide is the highest,which is 376 HV_0.1,compared to wheel steel cladding without nano-cerium oxide and unclad wheel steel substrate,the average surface hardness increased by 15.3%and 30.1%,respectively.The average surface hardness ratio of the wheel steel cladding layer with 1.5%nano-cerium oxide to the rail steel substrate H_W:H_R?1.15:1.00,which meets the requirements of modern wheel/rail hardness matching.After adding 1.5%nano-cerium oxide,the wheel steel cladding layer has the best effect of improving the discharge corrosion resistance.Under this test condition,the optimal amount of nano-cerium oxide is 1.5%.(3)The thermal performance of the wheel steel cladding layer is better than that of the wheel/rail steel substrate.The discharge corrosion rates of the wheel steel cladding layer after laser cladding modification and the paired rail steel substrate are 0.0045g/min and0.0017g/min,respectively,Compared with the unclad wheel/rail substrate,the discharge corrosion rate decreased by 84.7%and 61.1%,respectively.Surface cracks of modified wheel/rail materials discharge corrosion are significantly reduced,and pits become smaller and shallower.The main phases of the wheel steel cladding surface after discharge corrosion are(Cr,Fe)₂O₃ and Ni Cr₂O₃,and the main phases of the wheel steel and rail steel substrate after discharge corrosion are Fe₃O₄ and martensite.After discharge corrosion,the microhardness and average surface hardness of the modified and unmodified wheel/rail material increased significantly.The hardness ratio of modified wheel/rail materials after discharge corrosion meets the requirements while the hardness ratio of unmodified wheel/rail materials after discharge corrosion does not meet the requirements.After laser cladding modification,the anti-discharge corrosion performance of the wheel steel cladding layer and the matched rail steel substrate have been greatly improved.The volume wear rate and friction coefficient of the wheel steel cladding layer are reduced compared to the wheel steel substrate.The volume wear rate of the wheel steel cladding layer is 9.247×10^-5mm³/m,and the volume wear rate of the wheel steel substrate is 2.9456×10^-4mm³/m,compared with the wheel steel base material,the wheel steel cladding layer is reduced by 68.8%.The wear mechanism of the wheel steel substrate is mainly abrasive wear and fatigue spalling,and the wear mechanism of the wheel steel cladding layer is mainly oxidative wear and slight abrasive wear.The wear resistance of the wheel steel cladding modified by laser cladding has been significantly improved.