Study On Microstructure And Property Of Ni60（WC）/Ni60（Cr₃C₂） Coating With High Velocity Oxygen-fuel Spraying

Ni60 powder,WC-Co powder and NiCr-Cr3C2 powder were selected to improve the wear and corrosion resistance of the ball valve surface under complex working conditions,Ni60（WC） and Ni60（Cr₃C₂） composite coatings were prepared on the surface of 45 # steel with High Velocity Oxygen-fuel Spraying,the mass fraction of WC and Cr3C2 were 12.5%,25% and 37.5%. The surface morphology, component,porosity, microstructures, microhardness, friction and wear properties and electroch-emical corrosion resistance were examined by scanning electron microscopy（SEM） ,energy dispersive spectrometer（EDX） with scanning electron microscope,optical microscope（OM）, X-ray diffraction（XRD）, Vickers hardness tester, the material surface tester（HSR-2M） and electrochemical workstation（VersaSTAT4）. The friction and wear behavior of the coating under different conditions such as friction pair and load were investigated. The microhardness, wear resistance and corrosion resistance of Ni60（WC） and Ni60（Cr₃C₂） coatings were compared and discussed,The results show:（1）Ni60（WC） and Ni60（Cr₃C₂） coatings were prepared with High Velocity Oxygen-fuel Spraying, The coatings were layered by SEM observation , the structure is dense and uniform, The matrix is well combined, the porosity is low.The main phases of Ni60 （WC） coating are WC, Ni3Fe, WC, Cr3C2, W2C and so on. Grain fine WC particles with high hardness and uniform dispersion in the coating, Friction and wear experiments show that: With the increase of WC content, the hardness of the coatings are improved, The less volume wear, wear resistance is the better, The abrasion resistance was in the order of Ni60 （37.5%WC）> Ni60 （25%WC）> Ni60（12.5%WC）.Under low load, the performance are surface fatigue wear and brasive wear. Under high load, the main wear mechanism of the coating are surface fatigue wear and adhesive wear. Cryogenic experiments show that:After cryogenic treatment can effectively improve the hardness and wear resistance of Ni60（WC）coating,Ni60（Cr₃C₂） coating after cryogenic wear performance is almost unaffected. In 5%H2SO4 medium,The electrochemical test show that:The corrosion resistance of the coating is increasing with the increase of the WC-Co mass fraction in the Ni60 （WC）coating. The WC-Co mass fraction is in the range of 12.5% -37.5%, the corrosion resistance of Ni60 （37.5% WC） is best.（2）Ni60 （Cr₃C₂） coating main material phase Cr3C2, Cr7C3, Cr23C6 and other hard phase and Ni-Cr bonded phase, During the spraying process, carbides in the powder under the action of high temperature flame produce a little decarburization.Friction and wear experiments show that: The hardness of the coating increases with the increase of Cr3C2 content,The order of wear resistance isNi60 （37.5%Cr3C2）> Ni60（25%Cr3C2）> Ni60 （12.5%Cr3C2）. under low load,Wear mechanism are fatigue wear and , in the condition of high load, which is surface fatigue wear and a certain degree of adhesive wear. Electrochemical corrosion test proved: in 5%H2SO4 medium,The addition of Cr3C2 in Ni60 powder can improve the corrosion resistance of the coating,and with the improvement of Cr3C2 mass fraction, the better the corrosion resistance of the coating.（3）Ni60 （WC） coating is obviously higher than that of Ni60 （Cr₃C₂） coating because of the high density and high hardness of WC, and the partial load of WC particles during friction and wear makes the volume loss of Ni60 （WC） Less wear resistance is better, wear resistance of Ni60 （37.5%WC） is best. Ni60 （Cr₃C₂）coatingporosity is lower than Ni60 （WC）, corrosion current density is small, test show that: Ni60 （37.5% WC） coating and Ni60 （37.5% Cr3C2） coating showed good corrosion resistance in H2SO4 medium with 5% volume fraction.