Process And Wear Resistance Of Ni-CeO₂ Nanocomposite Coatings By Electrodeposition With Ultrasonic Irradiation

Nanocomposite coating can be produced by electrolytic or electroless codeposition, which inert nanoparticles (1～100nm) suspended in the bath are codeposited with the metal to form the composite coating. Rare earth oxides nanoparticles register many special characteristics due to collecting the properties of rare earth element and nanoparticles effect. Nanocomposite coating may exhibit many special properties while the rare earth nanoparticles are added into the electrolyte during electrodeposition. However, because the rare earth nanoparticles were easy to form the agglomeration during electrodeposition, the properties of the nanocomposite coating decreased. How to promote the uniform dispersion of nanoparticles in coatings is a difficult problem, which should be handled in the present electrodeposition technology. Ultrasound dispersion is one of effective methods of reducing the agglomeration of the nanoparticles, which not only can easily promote the uniform dispersion of the nanoparticles and refine the crystals of the nanocompsotie coatings, but also strengthen the electrodeposition process, enhance the electrodeposition velocity and current efficiency.In this paper, Ni-CeO₂ nanocomposite coatings were successfully produced by ultrasonic electrodeposition combining the ultrasound and nanocomposite electrodeposition. The process of producing Ni-CeO₂ nanocomposite coatings by ultrasonic electrodeposition was investigated, with the effect of the technological parameters on the CeO₂ content in the coatings to be emphasized. The effect and the action mechanism of the ultrasound action and the nanoparticles on the micro structure and properties of the coatings were analyzed by means of the observation of surface morphologies and microstructure as well as the test of the microhardness and tribological properties of the coatings. The main contributions are presented as follows: (1) The optimum process parameters of preparing Ni-CeO₂ nanocomposite coatings with ultrasound irradiation were obtained. The effects of process parameters, such as addition content of particles, ultrasound power, current density and electrolyte temperature, on the CeO₂ content in the coatings and surface morphologies of coatings were studied. The coating prepared with optimum process had smoother morphology, more compact microstructure and finer crystal grain compared to the coatings produced under the other process parameters.(2) The effects of ultrasound and CeO₂ nanoparticles on the crystal preferential orientation and crystal structure of coatings were investigated. The crystal growth was gradually preferred towards (1 1 1) and (3 1 1) orientation with the increase of CeO₂ content in the coatings. When the power of ultrasound increased, the crystal preferential orientation of coatings gradually grew towards (2 2 0) orientation. It was also shown that the ultrasound action can refined crystal grain obviously.(3) The effects of ultrasound and CeO₂ nanoparticles on the microhardness and wear resistance of coatings were studied. The ultrasound and the CeO₂ nanoparticles could remarkably enhance the microhardness of nanocomposite coatings. Wear rate of the Ni-CeO₂ nanocomposite coatings gradually decreased with the increase of the CeO₂ content in the coatings. The wear rate of the Ni-CeO₂ nanocomposite coatings could be reduced due to the ultrasound action in the electrodeposion process. The improvement in wear resistance of the coatings is mainly attributed to the ultrasound and then to the CeO₂ nanoparticles.(4) Improvement mechanism of ultrasound and CeO₂ nanoparticles on the wear resistance property of coatings were analyzed. Dispersion strengthening effect of CeO₂ nanoparticles in the coatings enhanced the microhardness of coatings, decreased the wear rate of Ni-CeO₂ nanocomposite coatings. The ultrasound in the electrodeposition progress improved the uniform dispersion of the nanoparticles in the electrolyte and in the coatings, as well as refine the grain of nanocomposite coatings, thus improved the wear resistance of coatings.The processes of producing Ni-CeO₂ nanocomposite coatings with excellent wear resistance by ultrasonic electrodeposition were obtained. The work of this research will play the instructive role in exploiting the nanocomposite coatings with high performance and solving the nanoparticles agglomeration in the electrodeposition technology.