Fundamental Investigation Of Rare Earth Nanocomposite Electroforming Technology Under Dual-frequency Ultrasound

The composite electroforming deposits prepared by the nanocomposite electroforming technology have excellent properties, such as high microhardness, high-temperature resistance, corrosion resistance and wear resistance, which can be used to enhance the comprehensive properties of electroformed parts. Dual-frequency ultrasound with a good synergistm and strong cavitation effect, can effectively inhibits the aggregation of nanoparticles in electroforming bath, refine the grain of electroforming deposits, and thus improve the microstructure and properties of the electroforming deposits.In this dissertation, the fundamental research of rare earths nano-composite electroforming technology under dual-frequency ultrasound was carried out, using Nd₂O₃ nanoparticles as suspended particles in electroforming bath. Effects of the addition of rare earths nanoparticles, current density and ultrasonic power and frequency on the nanoparticles content in composite electroforming deposits were investigated. The electroforming process of preparing Ni-Nd₂O₃ nanocomposite electroforming deposits were obtained. The microstructure of the composite electroforming deposits were analyzed. The microhardness, corrosion resistance, high temperature oxidation resistance and friction and wear characteristics of the electroforming deposits were studied.Effects of the process parameters, such as the addition of nanoparticles, the cathode current density, the power and frequency of bath-type ultrasonic as well as the power and frequency of probe-type ultrasonic, on the Nd₂O₃ nanoparticles content in the nanocomposite electroforming deposits were investigated. The suitable process parameters of preparing Ni-Nd₂O₃ electroforming deposits prepared by electrodeposition under dual-frequency ultrasonic were obtained. The suitable process parameters are as follows: Nd₂O₃ nanoparticles concentration 40g/L, cathode current density 4A/dm2, bath-type ultrasonic power 240W, bath-type ultrasonic frequency 100kHz, probe-type ultrasonicpower 30W, probe-type ultrasonic frequency 20kHz, electrolyte temperature 45°C, stirring speed 1000r/min.The effect of the process parameters, such as addition of nanoparticles, current density, bath-type ultrasonic power and frequency, probe-type ultrasonic power, on the surface morphology of the nanocomposite electroforming deposits were studied. The surface morphology of the pure Ni and the nanocomposite electroforming deposits obtained by direct current, single-frequency and dual-frequency ultrasonic were analyzed comparatively. The Ni-Nd₂O₃ nanocomposite electroforming deposits using dual-frequency ultrasound shows smooth surface, compact structure and finer grains.The crystallization orientation of Ni deposits and the Ni-Nd₂O₃ nanocomposite electroforming deposits obtained by direct current, single-frequency and dual-frequency ultrasonic were investigated comparatively. The effects of bath-type ultrasonic and probe-type ultrasonic on electroforming deposits crystallization orientation were mainly analyzed. The dual-frequency ultrasonic could change the preferred orientation of the crystallized grains.The microstructure of Ni deposits and the Ni-Nd₂O₃ nanocomposite electroforming deposits obtained by direct current, single-frequency and dual-frequency ultrasonic were investigated comparatively. The Ni-Nd₂O₃ nanocomposite electroforming deposit prepared by dual-frequency ultrasound exhibits finer grain, uniform structure, and the Nd₂O₃ nanoparticles is bonded tightly to Ni matrix.The microhardness, corrosion resistance, high-temperature oxidation resistance, friction and wear properties of nanocomposite electroforming deposits were investigated. Owing to the application of ultrasound, the comprehensive properties of Ni-Nd₂O₃ nanocomposite electroforming deposits were markedly improved. The Ni-Nd₂O₃ nanocomposite electroforming deposit prepared under dual-frequency ultrasound exhibits high microhardness, excellent corrosion resistance, strong high-temperature oxidation resistance, good antifriction and wear resistance.The electroforming process of Ni-Nd₂O₃ nanocomposite electroforming deposits with excellent properties has been obtained through experimental research in this dissertation. This research will be scientific guiding significance for the application of dual-frequency ultrasound in composite electroforming.