Study On TiC/NiCrBSi Cladding Layers By Laser Cladding In-situ Fabricated On The Surface Of Oil Well Pump Plunger

With most of the domestic oil field entering the high watery development period,corrosive wear of oil well pump is increasingly serious due to the effect of high content of sand,water and salinity,high temperature steam heavy oil mining,polymer injection and strong corrosion medium,which seriously affects the exploitation of oil fields.In this research,the Ni-based cladding layer reinforced by in-situ fabricated TiC by laser cladding on the surface of oil well pump plunger.The microstructure,wear and corrosion properties of the cladding layer were analyzed systematically as well as the interfacial properties between TiC and metal substrate and the main factors influencing microstructure and properties.The reasons of failure on the surface of oil pump plunger are various.Sand deposition in the pump will lead to the scratch of the surface of plunger; the liquid with sand under high pressure difference will cause the incising; the increased pump setting depth will result in the increase of friction force between the pump barrel and the plunger; the local corrosion and wear between the pump barrel and the plunger is more serious due to the non-vertical structure of the well; high temperature underground aggravates the corrosion and scaling of the pump barrel and the plunger.The failure mechanism of the plunger surface is abrasive wear,corrosion wear,sticking and corrosion.Abrasive wear mainly includes gouging abrasive wear,erosion wear,grinding wear and tear,scratches wear and jet wear.Corrosion mainly includes galvanic corrosion,uniform corrosion and fatigue corrosion.The main failure of the plunger surface is corrosion and abrasive wear.Through adding Ti and graphite powder to Ni35 or Ni60,the Ni-based cladding layer reinforced by in-situ TiC was prepared by laser cladding. The cladding layers have an excellent metallurgical bonding with the substrate.The volume fraction of TiC particles increases successively from the bottom to the top of the cladding layers,and the particle size changes gradually from the nanometer to micron level.The hardness of the cladding layer decreases from surface to substrate of the cladding layers,and the hardness of the TiC/Ni60-based cladding layer is much higher than that of TiC/Ni35.The bonding interface between TiC phase and the solid solution(Fe,Ni) is clean without reactants and attachments,and the coherency and compatibility of these two phases is excellent.There is a great deal of dislocation in TiC particles,which distributes in some direction.The laser cladding technology is also the important factor influencing the microstructure and properties of the Ni-based TiC composite cladding layer. The results show that the cladding layer with good appearance,low dilution rate and high hardness could be obtained when the thickness of the pre-coated powder is 1mm,scanning speed is 150mm/min and cladding power is 3500W. The laser cladding with three layers can effectively reduce the dilution rate of base metal to the cladding layers,increase the quantity and size of the TiC reinforcement in cladding layer,and get petal-shaped and granular TiC particles,which are beneficial to get the uniform cladding layer with high hardness.Cracks in TiC/NiCrBSi cladding layers are mainly cold brittle cracks resulted from low ductility of the cladding layer due to the existence of M23C6 phase and residual internal stress.Through decreasing the carbon content of the cladding layers by means of reducing the graphite content of the powder,the microstructures of the cladding layers can be improved,plasticity and toughness can be enhanced,and residual stress can be decreased,therefore,the cracking susceptibility can be reduced.As for the ceramic phase segregation in the microstructure of the cladding layer,this phenomenon can be obviously lightened and even disappear by adding Mo to the cladding layer.Mo can improve the interfacial wettability of TiC phase to Ni-base phase,which makes TiC particles dispersedly distribute in the Ni-based solid solution phase.This contributes to impeding the accumulation and growth of TiC during the process of in-situ fabrication,improving uniformity,rigidity,wear resistance,refining TiC grains,reducing friction coefficient.However,the hardness and wear resistance of cladding layer decrease with the addition of excessive Mo.The corrosion and wear resistance of cladding layer can be improved through adding appropriate content rare earth to the cladding layer. La and trace of impurities in the molten pool form the tiny compounds with complicated components,which can be considered as non-spontaneous nucleation particles.These particles contribute to increasing nucleation cores,refining grains and cleaning the structure of the cladding layers,and increase the hardness and wear resistance can be improved.Meanwhile electrode potential can be improved while corrosion current can be reduced by LaF3,The corrosion resistance of cladding layer can be improved.Wear test indicates that three-layer claddings make reinforcement performance of TiC particles more effective and have excellent wear resistance property. Wear-resistant hard particles on the surface of TiC/NiCrBSi cladding layers hinder the extension of the wear scar,and the hindering and pinning action prevent the wear seriously,so that the wear loss of TiC/NiCrBSi cladding layers decreases remarkably.The main wear mechanism of cladding layers matrix is microdissection and adhesive wear.Wear resistance of TiC/NiCrBSi cladding layers is better than that of Ni60 cladding layers with the reason of the former's lower friction coefficient.Compared with Ni60 cladding layers,TiC/NiCrBSi cladding layers have higher electrode potential,but higher corrosion current.TiC/NiCrBSi cladding layers can improve the corrosion resistance of the carbon steel matrix,and have lower uniform corrosion resistance and higher local corrosion resistance than Ni60 cladding layers.During the experiment of corrosion wear,TiC particles in TiC/NiCrBSi cladding layers play the roles of enhancement and frictional resistance.Corrosion happens preferentially on grain or phase boundaries,and weakens the adhesive force between TiC particles and the matrix.As a result,corrosion aggravates the wear and TiC particles fall off more easily due to the wearing action.Corrosion wear morphology is cutting plough ditch and etch pits.The mechanism of corrosion wear is corrosion abrasive particle wear.It is because wear predominates over corrosion under this working condition that corrosion wear property of TiC/NiCrBSi cladding layers is better than that of Ni60 cladding layers.