Fundamental Research On Manufacturing Technology And Properties Of Ni-Based Nano-composite Coatings By Electrophoretic-electrochemical Deposition

Nano-composite coatings are widely studied because of its excellent physical mechanical properties. The nano-composite coating is prepared mainly by nanoparticles codeposition with matrix metal at present. Because only a few nanoparticles were embedded in the coatings by this method, the properties of the coatings is unable to be improved significantly.In this dissertation, a new technique, electrophoretic-electrochemical deposition, was proposed to produce nano-composite coatings with high content of nanoparticles. A uniform film of nanoparticles was first electrophoretically deposited on a substrate, the matrix metal was then electrodeposited onto the substrate covered with the film of these nanoparticles. By adopting this method, the nano-composite coatings with 15~60vol% of nanoparticles can be obtained. The properties of the coatings can be improved efficiently because plenty of nanoparticles exists in the coatings.The main researches and conculsions are given as follows:1. The researches on electrophoretic deposition of nanoparticles were carried out. The influence of the process parameters on the deposition weight and dispersion state was studied, the deposition layer with uniform distribution and well dispersed nanoparticles was produced by optimizing the dispersant.2. The process of electrophoretic–electrochemical deposition was studied. Through analyzing the changes of the nanoparticles distribution state, a phenomenon was observed that nanoparticles was disturbed and redeposited at the electrodeposition process. The effects of the parameters on the particle content and the nanoparticles dispersion state were systematically analyzed, and the maximum thickness of the composite coatings was studied.3. Surface morphology, component, and microstructure of the nano-composite coatings were examined. The effects of process parameters on the micro-morphology of the nano-composite coatings were investigated. With the mean square deviation of the particle content in the micro-region as an evaluating index, the effects of the parameters on the distribution uniformity of the particles were studied by orthogonal test. Meanwhile, the crystal orientation of matrix metal and microstructure of nano-composite coatings were examined. The results indicated that, the main factors that influenced the particles distribution state were the concentration of nanoparticles in electrophoretic bath and the current density at the electrodeposition process. The nano-composite coatings exhibit a smooth surface and compact microstructure. Nanoparticles are dispersed inside the metallic matrix and combined with the metallic matrix closely. In electrodeposition process, nanoparticles affect the preferred orientation of matrix metal remarkably.4. The properties of the nano-composite coatings, such as microhardness, wear resistance, corrosion resistance and adhesion strength were evaluated. The results showed that the microhardness and wear resistance of the nano-composite coatings were significantly increased, and the major wear pattern under dry friction conditions was abrasive wear mechanism. Compared with pure Ni coating, the corrosion pits of the nano-composite coatings become smaller and more uniform. The bonding strength is related to the particle content, when the particle content is in a certain ratio, adhesion strength of the nano-composite coatings is better than the pure metallic coating.