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To improve the surface quality and performance of Ni-SiO 2 nanocomposite coatings, jet electrodeposition of SiO 2 nanoparticles (diameter 20-30 nm) with Watt's nickel solution was used to process on graphite substrate accompanied by ceramic stick rolling and friction (R&F) online. The crystal structure and microstructure of coatings were analyzed by using X-ray diffraction and field emission scanning electron microscope, respectively. The corrosion resistance of the samples was evaluated by potentiodynamic polarization (Tafel). By studying the influences of different concentrations of SiO 2 in the solution and the effect of R&F on the coatings, we found that adding a certain amount of nano-SiO 2 in the solution can significantly increase the microhardness of coatings (from 550 HV to 627 HV or a 14% increase). R&F further caused the microhardness to reach 711 HV, which is a 20% increase relative to pure Ni coatings. Moreover, R&F can help to remove cellular bulge on the surface of nanocomposite coatings, thereby improving surface quality. The corrosion resistance of Ni-SiO 2 nanocomposite coatings is better than that of pure Ni coatings. In recent years, nanocomposite coating processed by electrodeposition has received widespread attention because it performs better than pure metal coating.1-2 In the process of electrodeposition, nanoparticles deposited in the coating as the second phase, thereby improving the performance of the coating.3-13 P. Baghery 14 obtained Ni-TiO 2 nanocomposite coating by using electrodeposition, which greatly improved the wear resistance and corrosion resistance of the coating. Ping Yu 15 improved the high-temperature oxidation resistance of Ni coatings by adding nano-SiO 2 to the solution. Yi Wang 16 obtained a Ni-W-SiO 2 coating by direct electrodeposition, which increased the microhardness by nearly 60 HV but worsened the surface quality.Ni-based coating is widely used as a protective layer for various mechanical instruments because of its excellent anti-corrosion property, wear resistance, high hardness, and good appearance. 1,6,8 Our team has conducted related research on this coating for years. [17][18][19][20] Nano-SiO 2 has a spherical microstructure, which can improve the strength and chemical resistance of materials. However, when nanoSiO 2 are deposited with nickel, the surface will form cellular bulges, 14 which influence the surface quality. Few studies focus on improving the surface quality of Ni-SiO 2 coating. To improve the hardness of Ni-based coating and solve the problem of cellular bulge, this paper proposes the use of jet electrodeposition to process nanocomposite coatings accompanied by ceramic stick rolling and friction (R&F) online. R&F prevents reunited particles from depositing into the coatings and removes surface bulge, thereby improving the quality of the coatings. ExperimentalExperimental device.-The experimental device is shown in Figure 1. The workpiece is fixed in a plating bath with a special fixture as the cathode. Plating solution is pumped into the a...

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Medium-voltage (e.g. 10 kV rated) silicon carbide (SiC) devices have great potentials in medium-voltage variable speed drives. But their high switching dv/dt can increase the voltage stress on motor windings and cause partial discharges. This paper presents a partial discharge study of a medium-voltage form-wound winding under two-level square-wave voltage pulses. A 10 kV SiC device-based test platform is built to generate voltage pulses with high dv/dt. A three-step test approach is proposed and employed to systematically investigate the effects of various voltage parameters on partial discharges. These include voltage rise/fall time, voltage pulse width, pulse repetitive rate, duty ratio, voltage polarity, fundamental frequency, and modulation index. Partial discharge inception voltages (PDIVs) and repetitive partial discharge inception voltages (RPDIVs) of the sample are measured with varied voltage parameters. Test results show that voltage rise/fall time is a major affecting factor which reduces PDIVs of the winding sample by 6.5% when it decreases from 800 ns to 100 ns. Based on test results, a hypothetical partial discharge mechanism is presented to explain the effects of fast voltage rise/fall edges. An empirical equation is also derived to estimate PDIVs of a winding sample under various voltage rise/fall time and pulse width conditions.