| Nickel-phosphorus (Ni-P) alloy coatings, with their high wear resistance, corrosion resistance and hardness, have an important role in extending the service life and reliability of engineering components, as well as in boosting the performance and quality of mechanical equipment. After thermal treatment, the hardness and wear resistance of Ni-P alloy coatings are comparable to those of chromium coatings, and their use in place of the latter would greatly reduce the environmental hazards caused by hexavalent chromium ions in the chroming process. Ni-P alloys have found wide application in the chemical, electronics, aerospace and automobile industries, for precision machinery, for mining machinery, and in a number of other areas.There are two main ways to obtain Ni-P alloy coatings, namely electroless plating and electroplating. The former boasts a wider range of applications and a more mature technology. However, the electroless plating process is more difficult to control and is expensive, and the plating solutions have a relatively short life, thereby producing a considerable amount of waste. In contrast, electrodeposition technology enjoys the advantages of simple operation, low cost, fast deposition speed, high bath stability, high production efficiency, thicker coating and low operating temperatures, among others. Moreover, it is easier to perform and control than electroless plating. But lower depositing rate and lower production efficiency are provided by the traditional electrodeposited Ni-P alloy method owning to the lower limiting current density. To meet the development needs of modern production, jet-electrodeposition is put forward in recent years, which significant increase in depositing rate and production efficiency. Because jet electrolyte can accelerate transfer process of the electrodeposition material and augment limiting current density. Above all, the jet electrodeposition is kind of high-velocity electrodeposition technique with high deposition current density and high depositing velocity. The basic principle of jet-electrodeposition is listed as follows. Through the anode nozzle, plating bath inject on surface workpiece, under the action of strong electric field, achieve the machining process of deposition. This research is meaningful to promote the development of high-speed plating.Based on Ni-P coating obtained by jet-electrodeposition on a 45 carbon steel substrate, this article mainly studied technology, electrochemical behaviour in the process of jet-electrodeposition and coating performance. Research works in this paper are summarized as follows:(1) Analysis on basic theory of electrode process kinetics. Based on electrode processes, kinetic equations under different conditions are focused analyzed including concentration polarization, electrochemical polarization as well as common concentration polarization and electrochemical polarization. Electrode process is studied mainly from the electric double-layer structure model, kinetics of electrode reactions and the characteristics of electrode polarization curve. It is provided theoretical guidance for electrochemical behaviour in the process of jet-electrodeposition Ni-P alloy.(2) Study on electrochemical behaviour in the process of jet-electrodeposition Ni-P alloy coating. Combining with basic processes and characteristics of induced codeposition, forming mechanism of jet-electrodeposition Ni-P alloy is analyzed. To prepare for subsequent in-depth theoretical study, the electrochemical behaviours in the process of electrodeposition Ni-P alloy are researched. Analyzing the comprehensive existing theories of jet-electrodeposition, dynamics parameters about electrode process of jet-electrodeposited Ni-P alloy are determined by using electrochemical analysis methods such as Tafel curves. And the mechanism of jet-electrodeposited Ni-P alloy is analyzed, which is validated by using AC (alternating current) impedance analysis of complex plane. Polarization type of jet-electrodeposition Ni-P alloy is studied by using cyclic voltammetry method, and cathode polarization behaviour in the process of jet-electrodeposited of Ni-P alloy is systematic analyzed. Theoretical analysis dynamic parameters, limiting current density and cathode polarization impact on alloy moulding. And through studying the kinetic of interfacial reactions, analysis additive effects on codeposition of Ni-P. Seek the action mechanism of additive, find effective ways to influence electrode reaction, causing the electrode reaction to a favourable direction and appropriate speed.(3) Study on computer simulation of jet-electrodeposition Ni-P alloy. The machining area between cathode and anode is used as research object and electric field and flow field of jet-electrodeposition process are researched. The mathematical model of the flow field in machining area is built according to liquid turbulent flow, and the mathematical model of electrodeposition, secondary is built according to electrodeposition with a moving geometry. The boundary condition is chosen according to the parameter of the jet-electrodeposition experiment. The influence of flow field and electric field distribution on actual machining is analyzed, and the profile curve of cathode growth at different time is simulated. The simulation results are verified by experiment of jet-electrodepositon. Finally, the structure of anode nozzle is optimized by analyzing electric field and flow field of machining area.(4) Study on technology experimental of jet-electrodeposition Ni-P alloy. Technological experimentation is investigated by using a custom design of JMP. Electrolyte temperature, voltage, dipolar space, flow velocity of electrolyte and dipolar relative velocity are the influence factors, and the depositing rate, Vickers hardness and surface roughness of deposited layers are the experimental index, and the relationships between the experimental index and the influence factors are analyzed through the response surface analysis method and sub-stepping method. The quadratic regression mathematical models that described the relations between the experimental index and the influence factors are established. The optimal technological parameters for coating performance are obtained through conducting multiple response optimizations by the method of expected function optimization. The results suggest that optimized prediction models of deposition rate, surface roughness and coating hardness are very significant. And fitting degree of three regression equations is very good, reliability of model is very high, prediction models have a certain application value. The optimal parameters are as follow:voltage of 15V, electrolyte temperature of 69 ℃, dipolar space of 1.5mm, flow velocity of electrolyte of 1.3 m/s, and dipolar relative velocity of 170 mm/min. Under these conditions, the depositing rate of deposited layer is 79.13um/min, the coating surface roughness is 0.375um, the coating Vickers hardness is 731.19HV, and their relative error is 0.36%、 1.4% and 0.64% separately, which illustrate regression models prediction for coating depositing rate, coating surface roughness and coating Vickers hardness is feasible.(5) Study on anti-corrosion mechanism of Ni-P alloy coating. The corrosion behaviour of Ni-P alloy coating in 50g/L NaCl solutions at different moment was studied by electrochemical impedance spectroscopy and potential scanning method. To get the corrosion mechanism of Ni-P alloy coating, using electrochemical analysis method summary corrosion regulation of Ni-P alloy coating dip in 50g/L NaCl solutions. The results suggested that corrosion resistance of Ni-P alloy coating decrease and then increase with the increase of immersion time. At first, the thickness of oxide layer is thinned in 50g/L NaCl solutions due to the attack of Cl-.After Oxide layer by Cl- penetration, Ni-P alloy will begin to dissolve. And then, the corrosion products are generated and gather on Ni-P alloy, which prevent the process of corrosion. The whole corrosion processes changed from activation control into diffusion control of Ni-P alloy coating and corrosion products. Obviously, Ni-P alloy coating prepared from jet-electrodeposition has excellent corrosion resistance. |
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