Study On Corrosion Resistance Of Ni-based Self-melting Alloy Coating For Ball Valve Under Different Working Conditions

In this paper,the corrosion resistance of Ni55A,Ni60A and Ni60C coatings for ball valves under different working conditions were studied.The coating materials used in this experiment included Ni55A,Ni60A and Ni60C,and the substrate material was 316L stainless steel.The coating was prepared by flame spraying and vacuum cladding technology.JMatPro was used to simulate the equilibrium phase diagram of the material and the element composition of each phase.XRD was used to analyze the composition of the prepared coating,and the test results were compared with the simulation results.The surface morphology of the coating was observed by SEM.According to the actual working conditions,the corrosion resistance and porosity of the coating were studied by using electrochemical workstation to simulate the actual working conditions.The material performance simulation software JMatPro was used to simulate the material composition and phase composition,which was consistent with the XRD test results of the actual experiment and provided a basis for the further experiment.From the XRD and SEM results show that the coating of precipitated phase of irregular though will cause the loss of corrosion resistance of the coating,but intergranular corrosion can avoid mainly because of the carbide is more,to a certain extent Cr7C3 Cr enrichment area,Cr23C6 and Cr3C carbide along the grain boundary precipitates,but after cladding coating cooling rate is fast,the precipitation Cr7C3,Cr23C6 and Cr3C less than,intergranular corrosion occurred less.The influence of temperature change on coating performance was studied.300g/L NaCl solution was used as electrolyte,and the temperature range was 40?90?.Electrochemical workstation was used to measure each sample.The experimental results show that when the temperature is 60?,several materials have relatively low corrosion rates and better corrosion resistance.However,as the temperature increases,Ni55A shows a sensitivity to higher temperatures and the corrosion rate increases significantly.Relatively speaking,Ni60A shows a downward trend of corrosion rate and better corrosion resistance at higher temperatures.About the corrosion resistance of the coating in different corrosive media,the sample was studied at 25? in different corrosive media of 0.1mol/L HNO3 solution,0.1mol/L H2SO4 solution,3.5%NaCl solution and 0.1mol/L NaOH solution.The experimental results show that Ni55A is more vulnerable to corrosion in acidic medium,and the corrosion rate in acidic solution is up to 6.8 times that in alkaline solution.According to the research on corrosion resistance of different coatings under actual working conditions,the samples were 316L,Ni55A,Ni60A and Ni60C,and the corrosion properties of the materials were studied at the temperature of 85? in the solution of 28%(NH4)2SO4+0.2%H2SO4 under the actual working conditions.The corrosion rate of Ni60A is 3.7 times that of Ni60C.At the temperature of 85?,Ni60C showed better corrosion resistance at 28%(NH4)2SO4+0.2%H2SO4 solution.The samples were Ni55A,Ni60A and Ni60C,and the corrosion properties of the material were studied at the temperatures of 63? and 71? of 31%oxalic acid solution.In the actual working condition,the corrosion rate of Ni55A is 6.69 times that of Ni60C.Ni60C showed better corrosion resistance at 31%oxalic acid solution at63?.The study on the surface porosity of ball valve ball core was carried out in the use of two different sealing agents.The red dots on the surface of the ball valve core represent the pores and other defects on the coating surface.The more red dots on the surface of the ball valve core,the denser it is,indicating that the surface pores and other defects of the sample arc more.The conchision can be drawn from the comparison of the experimental results of whether the surface of the ball valve core is coated with pore sealing agent.The use of the pore sealing agent can significantly reduce the porosity of the surface of the ball valve core,making the surface of the valve core denser and the corrosion resistance improved.Compared with the two-component epoxy resin seating agent,the singlc-componcnt epoxy resin scaling agent can improve the porosity of the coating surface better.