| Electrodeposited nickel-chromium alloy have attractive properties such as resistance to corrosion, good wear resistance and low resistance. Its performance is different because of different chromium content in the coating. When chromium content of nickel-chromium alloy plating reach a certain amount, they can form a protective amorphous structure of chromium on the surface. The corrosion resistance is equivalent or better than stainless steel with similar chromium containing. Electrodeposition of nickel-chromium alloy has the same performance with forging of nickel-chromium alloy. Instead of the chromium plating, it can be used for bearing, bush and other components required to resist against high temperature oxidation, and also for decoration.Add nanometer scale solid particles to the Ni-Cr plating and be fully dispersed, the nano-insoluble solid particles can suspend uniformly in the bath. They deposite in the coating with the co-deposition of Ni and Cr metal.Nanocomposite coating can greatly improve the hardness, wear resistance, corrosion resistance, friction reduction properties, high temperature performance, electricity and electro-catalytic properties.The main work consists of the following five parts:(1) The choice of the Ni-Cr plating systemBecause of the different potentials of nickel and chromium,to make co-deposition, we choose some different complexing agent in Ni-Cr plating. According to the results of the obtained Ni-Cr alloy plating, we select the appropriate Ni-Cr plating additives. Finally we select sodium citrate, sodium formate and urea as the complexing agent of the Ni-Cr plating.(2) The study of the technology of the Ni-Cr platingMake studies to sodium citrate -sodium formate-urea Ni-Cr plating system using DC plating method and in the orthogonal method, to assure the factors which impact the alloy plating. Finally we get the best combination of the Ni-Cr plating system. Make single condition experiment on the factors which affects the Ni-Cr plating system, choose the best condition of different factors.(3) The experiments of some kinds of properties of the solution and the coating of electroplating with Ni-Cr platingThe capability of Ni-Cr plating solution and Ni-Cr plating is the main target testing. The performances testing in the experiment are: the bath conductivity is 96mS/cm, the current efficiency is 60%, the dispersion of the bath is high. The Ni-Cr plating in DC plating have good appearance and strong binding,the porosity is five per square centimeter, the hardness can reach 1200～1300 HV. Add nano-TiO2 to the Ni-Cr plating by ultrasonic stirring. With the co-deposition of Ni and Cr, we obtain the nano Ni-Cr coating. Compared with the Ni-Cr plating, the nano-TiO2 Ni-Cr coating can greatly improve the hardness, wear resistance and corrosion resistance properties. The results show good performance of the Ni-Cr plating solution and Ni-Cr plating achieves the desired results.(4) The study of the continuous plating of Ni-Cr composite coatingsNi-Cr films were electrodeposited from a nickel sulfate, chromium chloride and chromium sulfate bath. To avoid the skin and poor adhesion of the continuous plating of the Ni-Cr alloy films, distilled water and DMF (volume ratio is 1:1) as the solvent is used.The addition of DMF in the nickel-chromium plating solution can cause overpotential, decrease the amount of cathodic hydrogen, make small changes in pH value. In addition, DMF can broaden the scope of plating current density, and then enhance the current efficiency.(5) The study of the polarization curve of the Ni-Cr plating solutionWe make researchs on the relationships between the polarization and the main salt, the bath acidity, additives and the temperature of the plating. According to the polarization curve, we know that the reaction of Ni and Cr is completely irreversible. Further, the study determines that the bath composition and the process conditions is reasonable in the Ni-Cr plating. |
PDF Full Text Request