Study On Microstructure And Properties Of Nickel-base Tungsten Carbide Composite Coating

The market demand of valves for chemical,steel and other industries has been increasing with the rapid development of China's petroleum refining,which the use environment and the requirements was more and more complex and strict.This article took precision valve of the304L stainless steel as the research object,with the goal of improving the wear resistance of the ball valve,adopted the oxygen-acetylene flame spray welding technology,the PVD multi-arc ion plating technology,and prepared on the surface of 304L steel with the ball valve and the same material of nickel-based tungsten carbide coating and nickel-based tungsten carbide composite coating of chromium nitride.The effects of different WC content of Ni60?WC?coating and Ni60?WC?-CrN composite coating on the microstructure,using XRD,SEM,EDS and other microstructure characterization methods,mechanical properties and friction and wear properties were studied.The effect of different WC content and CrN ion plating coating on the wear resistance of the valve was investigated.The main research work and conclusions of the paper are as follows:?1?The main components of Ni60?WC?coating are Ni₃Fe,WC,Ni₃Si,W₂C and Cr₂C₃alloy phases formed of Ni,Cr,Fe and C.The WC powder is dispersed in the Ni60 coating and could significantly improve its average hardness.The average hardness of Ni60?WC?coatings with WC content of 10%and 25%is HV886 and HV1025,respectively.However,promoting the WC content will increase the porosity of the coating.The porosity of the coating,WC content is 10%and 25%of Ni60?WC?,was 2.76%and 3.46%,respectively.The CrN film had a compact structure with a small amount of droplets and pits on the surface.It had a high hardness and can effectively increase the average hardness of the composite coating.The hardness of the Ni60?WC?coating is higher and the hardness of the Ni60?WC?-CrN composite coating is higher.The average hardness values of the 10%WC-CrN and25%WC-CrN composite coatings were HV1354 and HV1401,respectively.?2?The amount of wear decreased with the increase of WC content in Ni60?WC?coating under normal temperature friction,and the friction coefficient increased.The friction coefficients of 10%WC and 25%WC coatings under 5N load were 0.49 and 0.66,respectively.The friction coefficients with 7N load were 0.55 and 0.72,respectively,and the friction coefficients with 10N load were 0.59 and 0.62,respectively.Ni60?WC?-CrN composite coating under the same conditions?WC content,load?,compared with the Ni60?WC?coating wear loss,friction coefficient was also reduced,The friction coefficient of the5N load under 10%WC-CrN and 25%WC-CrN composite coating was 0.37 and 0.4,respectively.The friction coefficient was 0.45 and 0.41 for the 7N load and 0.5 and 0.42 for the 10N load.?3?The main wear mechanism of the coating is abrasive wear under 5N load in normal temperature friction;the main wear mechanism of the coating is abrasive wear and a small amount of adhesive wear under 7N load;the coating is mainly severe adhesion wear and slight fatigue wear under 10N load.The WC particles played a significant role in the coating,which reduced the wear of the Ni60 coating and increased the WC content.The Ni60 coating has reduced adhesion and abrasive wear.Ion-plated CrN film had a low friction coefficient,excellent anti-wear performance,reduced the friction coefficient of the composite coating,and inhibited the occurrence of adhesive wear and abrasive wear.The main wear mechanism of Ni60?WC?-CrN composite coating is fatigue wear and abrasive wear,which has better wear resistance at room temperature.?4?The wear of Ni60?WC?and Ni60?WC?-CrN coatings promoted with the increase of friction temperature.However,the wear of Ni60?WC?-CrN composite coating changed a little with 700°C and 400°C,mainly due to the Cr oxide Cr₂O₃ formed a protective film on the friction surface,which prevented drastic changes in the amount of wear.?5?The friction coefficient of Ni60?WC?coating at high temperature is related to the WC content.The higher the WC content was,the higher the friction coefficient was.The friction coefficients of the 10%WC and 25%WC coatings at 25°C are 0.48 and 0.53,respectively.The friction coefficients at 400°C are 0.41 and 0.58,respectively;The friction coefficients at700°C are 0.77 and 0.9,respectively.The friction coefficient of the CrN-Ni60?WC?composite coating is the largest at 25°C.The friction coefficients of the 10%WC-CrN and25%WC-CrN composite coatings are 0.35 and 0.42,respectively,and then decreased with increasing temperature.The friction coefficients of the 10%WC-CrN and 25%WC-CrN composite coatings were 0.29,0.47,and 0.34,0.4 at 400°C and 700°C,respectively,because Cr₂O₃ was formed during high-temperature friction and thus reduced.Friction resistance reduced the coefficient of friction.The friction and wear of Ni60?WC?and Ni60?WC?-CrN coatings at high temperature are mainly adhesive wear and abrasive wear.?6?The CrN film completely failed due to the plastic deformation and cracking of the CrN film under high temperature friction.When the cracks expand continuously,it will cause the flakes of the coating to fall off;in addition,the high temperature oxidation was also the main reason for the failure of the CrN film.Cr₂O₃ was formed with CrN film was oxidized,and it participated in friction and wear in the form of hard grinding debris.A furrow was formed on the surface of the coating,which caused abrasive wear and accelerated the destruction of the CrN film.?7?In the oxygen-acetylene flame spray welding of Ni60?WC?coating,increasing the WC content improves the corrosion resistance of the coating,The corrosion resistance of the Ni60?25%WC?coating is greater than that of the Ni60?10%WC?coating.The CrN coating prepared by the multi-arc ion plating technique can effectively improve the corrosion resistance of the Ni60?WC?-CrN composite coating.However,when the WC content increases,the performance of the Ni60?WC?-CrN composite coating decreases due to the CrN coating,and the corrosion resistance decreases.