| Nanocrystalline materials have been widely studied and applied because of its excellent performance.In many fabrication techniques,electrodeposition is a traditional,economic and flexible preparation method.Especially,jet electrodeposition has the advantages of fast mass transfer in liquid phase and high current density,which has a great advantage in the preparation of nanocrystalline metal materials.However,the deposition layer prepared by jet electrodeposition is prone to pinhole,pitting,nodulation and other defects,affecting the performance of nanocrystalline metal materials.Therefore,in order to quickly prepare high quality nanocrystalline metal materials,a movable,flexible friction jet electrodeposition(MFFJE)was proposed in this paper.On the basis of self-designed jet electrodeposition equipment and movable,flexible friction device,the mechanism of movable,flexible friction was further explored,and studied the influences of contact pressure,current density and cathode scanning speed on fabricating nanocrystalline nickel deposition.The main research contents are as follows:(1)Proposed the method of MFFJE.A set of jet electrodeposition equipment and a movable,flexible friction device were designed for this method,and a pressure detecting device that can detect movable,flexible friction contact pressure on-line was designed by using pressure sensors.At the same time,the displacement sensors were added to the moving directions of the equipment to ensure the stability of the equipment operation.The TFT resistance touch screen was used to realize the convenience of the operation.Finally,the design of whole control system was completed based on the control scheme of STM32+μC/OS-II.(2)Studied the mechanism of MFFJE.Based on the theoretical analysis of jet electrodeposition,fluid simulation software-Fluent was used to analyze the effects of adding movable,flexible friction near the nozzle on the liquid phase mass transfer and current density.In addition,through the previous comparative experiments,explored the mechanism of movable,flexible friction on the leveling layer,removing hydrogen and impurities,refining grain and so on.It was found that the movable,flexible friction has a good effect on improving the limit current density of the jet electrodeposition and improving the performance of the coatings.(3)Studied the effects of contact pressure of movable,flexible friction on the nanocrystalline nickel coatings′properties.The nanocrystalline nickel coatings were prepared under different contact pressures by using the designed pressure detection device.It was concluded that the contact pressure has an important influence on the performance of the deposited layer.When the contact pressure was controlled properly,the surface of the nanocrystalline nickel coating was smooth and dense,the grain size was refined to 13.5 nm,the hardness increased from 475 HV to 527 HV,and the corrosion resistance of the coating was also significantly improved.(4)Prepared nanocrystalline nickel bulk by MFFJE.Based on the previous research,further explored how to quickly prepare high quality nickel bulks and studied the effects of cathode scanning speed and current density on the properties of the deposited layer.The experiments showed that the movable,flexible friction can increase the available current density of jet electrodeposition to over 250A/dm~2,and the deposited layer remained flat and compact.Used the optimized processing parameters to prepare~1 mm thick nanocrystalline nickel bulks,and compared nanocrystalline nickel bulks prepared by with or without MFFJE.It is found that the movable,flexible friction has the ability to rapidly prepare high-quality nanocrystalline nickel bulk.The surface roughness of the obtained nanocrystalline nickel bulk was only 0.17μm and the hardness was up to 570 HV. |
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