Microstructure And Wear Properties Of Iron-based Graphite/MoS₂ Self-lubricating Coating By Laser Cladding

With the development of modern industry,many mechanical parts can not play a good role in lubrication under some extremely harsh working conditions.The solid self-lubricating coating can effectively improve the friction and wear resistance of the material surface.However,a single solid lubricant can no longer adapt to complex environment.In order to prepare self-lubricating coating which can adapt to the extremely harsh conditions,the iron-based graphite/MoS₂self-lubricating coating was prepared by using YAG solid-state laser with 40Cr steel as the base material.The effects of solid lubricant addition on the phase,microstructure,microhardness and friction and wear properties of the coating were studied.The tribological properties of iron-based graphite/MoS₂self lubricating coating were studied under high temperature.The results show that:(1)The optimum technological parameters of laser cladding iron base coating are:pulse width 6ms,scanning speed 180mm/min,current 200A,frequency 8Hz,defocusing amount 0mm,powder thickness 0.7mm,overlap rate of 50%.The cladding layer prepared by the optimized process parameters has no obvious cracks,pores and other defects,and the surface of the cladding layer is smooth and continuous.(2)The coating of iron-based alloy is mainly composed of?-Fe,Fe-Cr solid solution and cr_9.1si_0.9phase;the coating after MoS₂is mainly composed of Fe S,Cr S,?-fe and Fe-Cr solid solution.The phase of iron-based graphite/MoS₂self lubricating coating mainly includes M₂₃C₆,Cr₃C₂,Ni-Cr-Fe and Ni₃B.The content of S,Cr and C in the iron-based graphite MoS2 coating with Wt(Ni-G)=5%decreased gradually from the top to the bottom of the coating,and all of them were distributed on the branches.The graphite phase is distributed evenly on the coating surface with different graphite addition amount,and with the increase of graphite addition,the graphite phase on the coating surface increases.(3)The addition of MoS₂did not reduce the hardness of the coating.With the addition of Ni-graphite,the hardness of the coating has been improved obviously.The hardness of the coating with Wt(Ni-G)=5%of iron-based graphite/MoS₂reached 746.07 HV_0.2,which was about 100 HV_0.2higher than that of the coating without graphite.With the addition of Ni-graphite,a large number of hard carbides such as M₂₃C₆and Cr₃C₂are produced in the coating,which makes the hardness of the coating increase.However,with the increase of graphite addition,the dissolution degree of graphite decreases,and the proportion of soft graphite particles in the coating will increase,which leads to the decrease of coating hardness.(4)The addition of MoS₂greatly improves the wear resistance of laser cladding iron-based coating.In the self lubricating coating of iron-based MoS₂,the friction coefficient is the lowest when Wt(MoS₂)=3%,which is about 0.59,and the wear rate is2.56×10^-6mm³/N·m,which is only 5%of the wear rate of the iron-based coating.(5)At room temperature,when the addition of Ni-graphite is 5%,the friction coefficient and wear rate of iron-based graphite/MoS₂self-lubricating coating are the lowest,the friction coefficient is 0.54,and the wear rate is 1.15×10^-6mm³/N·m.the wear rate is 55%lower than that of the coating without nickel coated graphite,and the wear resistance and friction resistance are good.With the increase of temperature,the friction coefficient of iron-based coating,MoS₂coating and graphite/MoS₂coating gradually decreased.At 500?,the friction coefficient of graphite/MoS₂coating is 0.35 and the wear rate is 7.93×10^-5mm³/N·m.the friction reduction and wear resistance of the graphite/MoS₂coating are better than the other coatings.There are a large number of spalling pits and obvious furrows in the wear scar of the iron-based coating at 500?,and the wear is relatively serious.The wear mechanism is mainly adhesive wear.There are a lot of wear debris in the wear scar of the MoS₂coating,but no complete formation lubricating film.However,graphite/MoS₂coating forms a relatively complete lubricating film.The friction coefficient and wear rate of iron-based graphite/MoS₂composite coating are lower than those of iron-based coating with single solid lubricant MoS₂,which showed the synergistic lubrication effect.