Microstructure And Properties Of Nickel-based Tungsten Carbide Coating Cladding By Plasma Arc Cladding

Surface cladding technology is one of the important ways to improve the surface properties of mechanical parts in the fields of petroleum,chemical industry and construction machinery.It can not only repair the old parts,but also form a composite layer with special performance on the surface of parts,which can improve the surface quality,prolong the service life and reduce the cost of parts.Among them,plasma arc cladding technology has the advantages of full material melting,uniform distribution of thermal stress,low cost of equipment,easy operation and so on.Compared with other cladding technologies such as laser cladding technology,plasma arc cladding technology has incomparable advantages.The cladding coating made by adding tungsten carbide particles into Nickel-based self-fusing powder has higher hardness,better wear resistance and corrosion resistance,and is the best material for coating parts of petroleum,chemical industry and construction machinery.Therefore,in this thesis,the plasma arc cladding method was used to prepare Nickel-based tungsten carbide coating on the surface of Q345 steel.The microstructure and properties of the cladding coating were systematically studied.The main research results are as follows:The process of plasma arc cladding Nickel-based tungsten carbide coating was optimized by orthogonal experiment,and the influence of process parameters on the formation,dilution rate and hardness of the cladding layer was obtained.The results showed that through range and variance analysis,The main and secondary factors affecting the forming quality of the cladding layer were current>ion gas flow>cladding speed>powder feeding speed.The main and secondary factors affecting the dilution rate of the cladding layer were the current>powder feeding speed>ion gas flow rate>cladding speed.The main and secondary factors affecting the hardness of the cladding layer were the ion gas flow rate>current>powder feeding speed>cladding speed.The optimal process parameters were as follows:ionic gas flow 1.0L/min,powder feeding speed 18 cm³/min,cladding speed 2mm/s,current size 80 A.The effect of different WC content on microstructure and mechanical properties of Nickel-based WC coating cladding by plasma arc cladding was studied,and the dissolution mechanism of WC coating was explored.The results showed that the microstructure of Nickel-based WC coating was mainly composed of WC particles and Nickel-based binder phase,WC was WC and W₂C,and the Nickel-based binder phase contains Si C,Cr₂₃C₆,Ni₃Si,?-Ni and other phases.With the increase of the content of WC in the powder,the proportion of WC in the cross section of the cladding coating increases.When the WC content in the powder was 50wt.%,the number of WC particles in the coating was the largest and dispersed throughout the coating.The hardness of the cladding coating reaches the maximum of 1024 HV₁₀,and the wear resistance was the best.The whole sliding wear process was mainly composed of oxidizing wear,adhesive wear and abrasive wear.When the content of WC was low,the wear mechanism was mainly abrasive wear,and with the increase of WC content,the wear mechanism was mainly adhesive wear.The dissolution mechanism of WC particles in the cladding coating mainly includes partial dissolution and complete dissolution.With the increase of WC content,the proportion of WC particles in the cladding coating increases,and the microstructure morphology of WC edges and hard phase between WC particles changes from long strip or dendritic to massive.The effect of different contents of CeO₂on microstructure and properties of Nickel-based WC cladding coating was studied when CeO₂was added into powder.The mechanism of CeO₂was revealed.The results showed that there were no pores and cracks in the Nickel-based WC coating when CeO₂was added to the powder.The microstructure of Nickel-based tungsten carbide coating cladding by plasma arc was unchanged.The addition of CeO₂in the powder promoted the dissolution of WC particles,which made the shape of WC particles change from irregular to spherical,and avoided the WC edges Formation of cracks at angles.The microstructure of Nickel-based tungsten carbide coating was refined by plasma arc cladding.When the addition of CeO₂was 0.2wt.%,the best refining effect was achieved.Compared with the coating without CeO₂,the grain size of the Nickel-based tungsten carbide coating decreased by 67.3%.Correlative,with the increase of CeO₂content,the hardness and wear resistance of Nickel-based tungsten carbide coating firstly increased and then decreased.When the addition of CeO₂was 0.2wt.%,the hardness value reached up to 1139 HV₁₀and the wear rate was the lowest.Compared with the coating without CeO₂modification,the hardness increased by 20.5%and the wear rate decreased by 71%.The addition of CeO₂powder does not change the wear mechanism of Nickel-based WC coating.