| Conventional electrodeposition technology has been widely used for the preparation of functional coatings due to its low economic cost and easy control process. However, owing to the limitation of limiting current density and the influences by hydrogen evolution, adsorption of impurities, and protrusion discharge etc. factors at the cathode surface from an aqueous solution, deposition velocity of these coatings is slower, and the crystallization microstructure is usually much coarser. In addition, the pinholes, pits, nodulations and other defects are also easy to occur. Thus, the efficiencies, qualities and properties are not high.To meet the efficiency, quality, and performance requirements for electrodeposition products in modern industrial development, an universal meaning electrodeposition technology assisted by flexible friction was proposed, namely, the cathode surface was periodically scratched by flexible media with a certain strength and toughness in the electrodeposition of metals. The preparation parameters of the electrodeposited nanocrystalline nickel coating, the formation mechanism of nickel coating, the flexible friction mechanisms during the electrodeposition, and the properties of nickel coatings were researched using this technique from an additive-free Watts bath. Based on the technique, process and principle, an automatic electrodeposition system assisted by flexible friction was set up. Furthermore, its application in remanufacturing industrialization was explored.The experimental apparatus and an electrodeposition technology assisted by flexible friction was developed. The preparation parameters of the electrodeposited nanocrystalline nickel coatings were optimized. At the relative velocity of 12 m/min and the temperature of 50?, the smooth and dense nanocrystalline nickel coatings were prepared using bio-bristle flexible friction media with 30% coverage in the cathode. The nanocrystalline nickel coating has a (111) preferred orientation, the average grain size between 20-30 nm, the surface roughness of about 0.05 ?m and the microhardness between 470-500 HV.Initial growth mechanism of the electrodeposited nickel coating without friction is V-W model, and there is a epitaxial fine crystal growth zone; the formation process is in a coarse-grained columnar growth-oriented way. Initial growth mechanism for the electrodeposited nickel coating assisted by friction flexible is F-M mode, and the epitaxial growth is rarely observed; the formation process is in a layered nano-fine grain growth-oriented way.The microstructure of the electrodeposited nickel coating is improved by flexible friction behavior. The reasons of grain size refining to the nanoscale by flexible friction lie in increasing the nucleation rates and the adatom population, inhibiting surface adatom diffusion and breaking the aggregation growth of adatoms. The density of nano-twins are increased through relaxation of the high interfacial tension between crystallization atoms and reducing of the high interfacial energy. The structure take a transformation from the columnar crystal growth to the layered crystal growth by periodically inhibiting the discharge of metal ions at the pointed sites, and disturbing the growth of the valley region. In addition, the flexible friction could reduces the diffusion layer thickness, removes the adsorption of impurities, hydrogen bubbles, the oxide film at the cathode surface, and promotes the discharge growth of the metal ions in the valley, thus, increasing the allowed current density, eliminating hydrogen and impurity, activating the electrodes surface and leveling the coating.The chemical bond and a mechanical interlock connection between the coating and the substrate interface is strengthened through the activation of the substrate surface by flexible friction during pre-treatment process. Compared with the electrodeposited columnar nickel coating without friction, the electrodeposited nickel coating with layered structure assisted by flexible friction extend the propagation path of the corrosive media, making the corrosion proceed layer by layer. Thus, its corrosion resistance is enhanced. Nanocrystalline nickel coating increases the wear resistance due to its higher hardness, modulus of elasticity and the ratio of the both. Nano-twinned structure in as-deposited and annealing state reduces the driving force for grain growth, and improve its thermal stability. The microhardness of this coating is much higher than those of the coarse-grained nickel coating and the predicted by Hall-Petch relationship, thus its strengthening mechanisms include fine grain strengthening and twins strengthening.Based on the above-mentioned technology, process and theoretical knowledge, combined with the specific shaft parts, a horizontal automation electrodeposition system assisted by flexible friction was developed. The washing pen electroplated, the circulating bath, the automatic separating and recycling treatment solution etc. problems were solved in the system. Enter the size of the workpiece to be repaired and electrodeposition process parameters through the procedure control interface, then, full automation electrodeposition can be achieved. The automation electrodeposition system assisted by flexible friction has been used successfully to remanufacture the failure planetary carrier due to the corrosion/wear. It is easy to control the electroplating process, and the coating with a integrated and reliable quality is obtained. The system has a significant application and popularization value in remanufacturing shaft parts. |
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