Preparation And Investigation Of Self-lubricating Coating Of Multi-phases Carbon Structures Composite Cemented Carbide

Cemented carbide has the characteristics of high wear resistance and good red heat,which is widely used in the field of wear resistance,and the coatings prepared by cemented carbide are also receiving much attentions.Those coatings are widely used in tool materials,bearing materials and other fields.Cemented carbide coatings are usually hard,and cracks are likely to occur during long-term loading and service,causing the coating to fall off over a large area.Adding a solid lubricant to the cemented carbide coating can reduce the friction coefficient of the interface during the service process,and this effect would be effectively improved if the cemented carbide coating can continuously produce a lubricating action during wearing process.The study is to develop and prepare a low-cost carbon-containing self-lubricating wear-resistant coating of cemented carbide,which could be applied on large-scale bearing workpieces.In the present work,graphite is used as a lubricant raw material,and two different methods are applied to prepare a graphene-containing multi-carbon structure lubricating cemented carbide coating,as,(1)deposition by plasma spraying(APS)plus modification with the high current pulsed electron beam(HCPEB)irradiation;(2)preparing embedded nano-graphene / micrometer cemented carbide core-shell structure,and directly deposition with APS.The microstructure,phases structure as well as the microhardness and wear resistance of the coatings were observed to compare the application scopes of these coatings prepared with the two fabricating methods.Results are as follows,(1)Graphite with 6wt.% content was added into a YG6 cemented carbide coating.After HCPEB irradiations,the thickness of the modified layer was over 180 ?m.With the increase number of pulses(1-30p),the flatness of the coating surface gradually increases.After 20 P,the flatness of the coating is the best.After 30 P,the coating craters increase and the density decreases.After modification,a dense submicron Co3W9C4 structure and WC structure were formed on the surface of the coating.At the same time,the original coarse graphite flake structure(500 ?m)became smaller(10 ?m)and was converted into graphene.On the coating surface,in addition,a small amount of diamond structure(1 ?m)was also observed on the coating surface.The improvement of the coating's compactness,the microstructure becomes finer and smaller,as well as the formation of diamond structure,had contributed to the significantly increases of microhardness,~800 Hv,and the value would be over 2000 Hv in some local areas.The formation of nano-graphene and the continuous lubrication of the multi-carbon structure had led to the decrease of friction coefficient(<0.1)after 1 hours of dry friction.(2)Graphite(500 ? m)was exfoliated in situ to form graphene(300-500 nm)by high-energy ball milling,and the graphene were embedded in the porosity's locations of YG6 cemented carbide powder(40 ? m)to form a core-shell package structure.The core-shell powder(graphite/graphene of 3wt.% and 6wt.%)were effectively deposited in the coating by APS,and the deposition rate was 65-80%.The coating mainly contained Co3W9C4 phase,WC phase,graphite and graphene,where the coating was dense and uniform,and the porosity was below 6.8%.Tests results showed that the microhardness of the coatings were ~ 750 Hv,as well as the friction coefficient was below 0.3 after a dry friction of 0.5h.(3)The self-lubricating coating of multi-carbon structure composite cemented carbide can be prepared in two ways,and the thickness of the coatings are more than 180 ?m,where the coatings are high density,good binding force and low friction coefficient,all those meets well with the requirements of wear-resistant applications.By spray shaping + HCPEB modification,the overall performance of the coating is excellent,but it is limited by the size of the vacuum chamber of HCPEB equipment;by the graphene embedded hard alloy core shell powder preparation + APS forming,the coatings are high molding efficiency,low cost,and low roughness(Ra5.5-7).The comprehensive performance and bonding force meet the needs of large wear-resistant parts.The second fabrication process is more suitable for an online wear-resistant coating repairing work of large bearings.