| Coatings with good wear-resistant prepared on the surface of the machine partshave emerged as an effective way to improve its service life. Compared with otherthermal spraying, arc spraying begin to be widely used for its advantages, such assimple device, convenient operation, higher efficiency and lower cost. The carbonalloying flux-cored wire is mainly used in the alloying arc sprayed coatings at present,but the adhesion strength and wear resistanc of this kind of coatings is lower for thecarbides is easy to grow and pee. In this article, element N was added into the wirebeing replaced parts of element C to be carbonitride alloying, and element V and Nbwere also added into the coatings to form carbonitride hard phase particles, which cangreatly improve properties of the coatings, especially the adhesion strength and wearresistanc. The research opened up a new path for arc sprayed resistant coatingsmaterials with good comprehensive properties.A new kind of carbonitride wear-resistant coating based on the basis alloyingcoating of the4Cr13martensitic stainless steel coating had been designed by addingCrN, ferrovanadium and ferrocolumbium. And arc sprayed flux-cored wires withgood performance had also been developed successfully. The precipitation behaviorof nitrogen in the coating had been studied, and the reasonable nitrogen content in thealloy was obtained. The results indicated that maximal nitrogen content in4Cr13steelis approximately0.10%, which can be up to0.20%after adding extremely a littlequantitiy of element V and Nb. The main reason that additions of Nb, V and Ti canincrease nitrogen solubility in the coatings are: first, they can reduce activitycoefficient of nitrogen in molten drop and increase its solid solubility; Second, as themost effective carbonitride forming elements added in the coating, these alloyingelements can enlarge nitrogen content. The transitional behavior of arc sprayed droplet was studied using high-speedvideo techniques, and effects on the coatings were also analyzed, the results showedthat the sizes of atomized droplets were different obviously when being sprayed, thebig droplet was about dozens of times than that of small one. The higher the value ofsprayed current and air pressure, the smaller the atomized droplets, the better theeffect of atomizing, and the higher the speed of atomized droplets. The highest speedof droplet was about78m/s, and the lowest speed of droplet was about21m/s. Theresearch on the droplet provided an effective way to analyzing and evaluating on thearc spraying process and coatings quality.The effects of mainly arc spraying process parameters of the spraying current,voltage, pressure and distance of the air atomizing on the microstructure andproperties of the carbonitride alloying coatings had been studied systematically. Theprocess parameters of arc spraying had been optimized. The effects of surfaceroughtening treatment of the workpiece, thicness of coatings and heat treatment onthe properties and microstructure of the coatings had also been studied. The resultsindicted that the optimal process parameters preparing carbonitride alloying coatingswere as follow:240A of current,30V of voltage,200mm of spraying distance and0.5MPa of the air atomizing pressure. The arc sprayed wire Ni95Al5was used toprepare the trasitional coatings, the thickness is about0.1mm, and the workingcoatings is about0.6mm. And550℃～650℃of tempering heat treatment canenharnce the comprehensive properties.The microstructure and properties of the carbonitride alloying coatings weredeeply investigated. The results showed that there are three main phases of the lathmartensite, the residual austenite and the hard phase particles distributedhomogeneously in metal matrix of the coatings. Coatings have compact structure andgood forming. Elements V and Nb can improve the microstructure and properties ofthe coatings. Coatings with4%ferrovanadium and6%ferrocolumbium had the bestcomprehensive properties, in which there were less porosity and oxides. The carbonitride alloying coatings had higher value of microhardness and adhesionstrength than that of4Cr13coatings, the average microhardness value is about556HV0.1, and the adhesion strength value reaches38.9Mpa. The value of abrasive wearperformance is about1.78times higher than that of the4Cr13coatings. After thetemper temperature of550℃, the hardness, the wear resistance and the adhesionstrength of the coatings had been improved, but the microstructure had not beenobviously changed.The carbonitride hard-phases in the coatings and the abrasive wear mechanism ofthe coatings were investigated and analyzed. The results indicated that carbonitrideparticles in the matrix of the coatings are complex MX distributing on the grainboundary or matrix, which sizes are smaller than3.5μm. M is the element of Nb, V orTi, and X is the element of C or N. The carbonitride can effectively refine themicrostructure, and hinder the crystal growing by fixing the crystal boundary. Thehomogeneous distribution of very fine carbonitride can not been easily disintegrated,which has precipitation strengthening effect on the matrix of the coatings. Thuscarbonitride could improve the strength and toughness of the coatings. The coatingswould have good abrasive wear behavior for the large quantities of carbonitrideparticles that precipitated out improving the microhardness of the coatings andhindering effective cutting of particles on the coatings.Formation mechanism of the carbonitride alloying coatings and influencingfactors on the coatings had been studied. Residual stress of the coatings was tested byXRD, which result was compared with that of the numerical simulation of the finiteelement method. The results indicated that there was the maximum value of residualstress on the interface between coatings and steel plate, which was compressive stress.Distribution and formation of the coatings had been successfully simulated by thenumerical analysis. And the result was the same as the order of XRD, which canprovide evidence to prevent and control the stress of the coatings, the value of theresidual stress was relative low which waw about1000MPa.Carbonitride alloying coatings were successfully prepared on the surface of theblade of the mixing drum for concrete mixer vehicle and the shaft of pump, the performance of the coatings had been tested by appearance analysis and scratch test,the results indicated that the coatings had high the wear resistance and adhesionstrength after long-time operation, which can meet the need of production. Therefore,the carbonitride alloying coatings have higher value of application and dissemination. |
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