| The human society civilization has gone through Stone Age,Bronze Age,Iron Age,Industrial Age,and Information Age,and then the Artificial Intelligence Age is right around the corner,which has gradually changed the ways of energy and material utilization.Compared with the inorganic materials and organic materials,metallic materials show excellent process ability and service performance,which makes the metallic materials play an irreplaceable role in the all kinds of materials.But there is certain limitation in metallic materials,for example metals tends to be corroded when it is in the environments with corrosive mediums and cannot have both good plastic property and high hardness.Metal surface treatment technology is an important way to improve the quality and property of the materials.Through the surface treatment,the surface has entirely different properties from the matrix,thereby the purpose of expanding application areas,economizing resource and reducing resources loss can be reached.Tungsten carbide particles are often used for surface modifying processing,because of excellent physical and chemical properties.There are some kinds of surface treatment technology based on tungsten carbide,including laser cladding technology,thermal spraying technology and brazing coating.But these methods have some disadvantages,for example the coating cannot form a metallurgical binding layer with its base metal,the coating bonding strength is low and there are biggish residual stresses in coating.In the present work,the preparation and properties of vacuum fusion Sintering Ni60-WC composite coatings on radial bearing were studied.The main tasks are described as following.(1)Preparation of “flexible alloy sheet”.Flexible alloy sheet is the biggest characteristic of vacuum fusion Sintering composite coating technology differing others.With the transformation of powder materials into flexible alloy sheet,on the one hand it can improve the utilization rate of raw materials,on the other hand it can elevate the adhesion of the coatings,that means vacuum fusion Sintering composite coating technology can be applied to any surfaces,like inner surface,outer surface and even special shaped surface.The influential factors of the alloy sheet property,like Ni60-WC content charge ratio and rolling parameters,are analyzed,and some conclusions are drawn.Under the optimized conditions(Ni60 content 40~50wt.%,rolling speed 2m/min,rolling reduction 50%,temperature 20~30 ?),flexible alloy sheet with smooth surface,thickness uniformity and compact structure can be prepared.(2)Vacuum Sintering process.Vacuum sintering process primarily resolves the problem how to get the metallurgical bonding between coating and matrix.This is a twostep process: phase one lets the organic compound additives in flexible alloy sheet be fully decomposed at around 550?,while Ni60 begins to melt and the coating gets the tendency of certain degree of free movement in phase two at around 1150?.(3)Property Evaluation of coating.This section is divided into three areas: bond strength,wear properties and corrosion resistance.The shear binding strength and tensile binding strength of the Ni60-WC coating ware measured through making different samples.The results show that the shear binding strength was 151 MPa and the tensile binding strength was 200 MPa.The wear resistance properties of coatings are evaluated by friction and wear tester,sliding against 45 steels in the quenched and tempered state.Surface hardness of the coating could get up to 950HV1,and coatings were of perfect scratch and abrasion resistance under a high coefficient of friction condition.The wear resistance property of Ni60-WC coating is 14 times more than the 45 steal.The corrosion resistance of the coating was characterized by polarization curves,the corrosion potential was-588 mV and the corrosion current density was 2.7?A/cm2,the coating corrosion resistance was between 45 steel and 304 stainless steel,and the coating can apply to common corrosive environments. |
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