Study On The High Frequency Pulse Plating Preparation Of Ni-Co-SiC Coating And Properties

The Ni-Co alloy coating prepared by a customized high frequency pulse power supply of20kHz-140kHz frequency has good stress and hardness properties, while in this experiment we add nano-SiC particles to prepare Ni-Co-SiC composite coating on the basis of the Ni-Co alloy coating. By changing the plating parameters methods, we try to improve the basic Ni-Co-SiC composite coating process, after repeated experiments as well as macro performance testing, metallograph, SEM analysis of the effects and reasons of various parameters on the composite coating appearance, we got a better technological conditions of high-frequency pulse plating Ni-Co-SiC composite coatings:nano SiC is8g/L, frequency is60kHz, average current density is3-4A/dm2, duty ratio is0.32, temperature is40degrees Celsius with additive0.5g/L sodium dodecyl sulfate boiled for30min and coumarin. As the appearance, hardness, corrosion resistance and other aspects of this coating is much better than the Ni-Co alloy coating, Ni-Co-SiC composite coating is a promising coating.The elements in Ni-Co-SiC composite coatings are analysisd by EDS in this experiment, the effects of the SiC content in the bath, pulse frequency, duty cycle, and current density to the SiC content in the coating was studied, from which we can calculate their effect to the Si element content in the coating. The grain size of the coatings is calculated by XRD, the rain of composite coating has been refined by adding nano-SiC, while there is no change in the crystal structure. SiC particles make the Ni-Co alloy coating (200) surface structure almost disappeared, the grain size of Ni-Co alloy coating is about30nm calculated by Scherrer formula, while the grain size of Ni-Co-SiC coating is about20nm, the grain size of high-frequency pulse plating has a decreasing trend after nano SiC particles added.The nano SiC particle content in composite coating is not the higher the better, the coating surface can be well refined when the content of nano-particles is SiC8g/L, the average grain size of the coating decreases as the content of nano SiC particle in the coating increasing, but the extent of decrease has been getting smaller and smaller. Deposition rate of the composite coating calculated is about70μm/h in the experiment, which is relatively faster than the speed of coatings without adding nano-SiC particles.The internal stress testing results indicated that increase the concentration of SiC in the bath within a certain range, increase the pulse frequency, reduce the current density and duty cycle with other parameters of the coating invariant will reduce the stress of the coating, as well as increase other appropriate of coating performance.The corrosion resistance of the high frequency pulse electrodeposited Ni-Co-SiC composite coating in10%NaCl solution and15%H2SO4solution is studied by weight loss method and anodic polarization curves. The Ni-Co-SiC coating has a good resistant of general corrosion, while there is not a very obviously increasing trend of weight loss when the SiC nanoparticles is increased in the bath. The polarization curves showed that the addition of nano SiC particles in composite coating can reduce the corrosion current density process and corrosion rate.The effects of hardness change of composite coating with different SiC concentrations in the bath are analyzed by Vickers microhardness tester. The addition of hard nano-SiC particles enhanced the hardness of Ni-Co composite coating, which increases at first, and started to show a downward trend when the concentration of nano-SiC in the bath reaches14g/L.