Research On The Preparation And Properties Of Nano-particles Enhanced Brush Plating Ni-W-Co Composite Coatings

The process parameters having an affect on the performance of brush plating coatingswere optimized in the orthogonal experiments, and then the Ni-W-Co coating which wascompact and high hardness was obtained. The optimum process parameters were chosen:brush plating voltage was 12-14V, the moving speed of electrode was 10m/min, pH ofplating solution was 1.5, and the concentration of complexing agent was 30g/L. Themicro-hardness of Ni-W-Co coating was 608HV, and the deposition rate reached1.82μm/min under the condition of optimum process parameters.The composite coatings with nano-particles were prepared by brush plating on thebasis of Ni-W-Co electrolyte. X-ray diffraction method (XRD), Scanning electronmicroscopy (SEM), DHV-1000 micro-hardness tester, electrochemical workstation andMM-200 tribological tester were employed to investigated microstructure, hardness andmorphology of composite coatings. The electrochemical corrosion behavior and wear andfriction characterization of the coatings were well studied, and electrochemical corrosionmechanism and wear and friction mechanism were discussed followed.The surface of the composite coating was smoother and flatter. The compositecoating's grain was smaller, and it combined well to the substrate. Both the compositecoatings and Ni-W-Co coat had crystal structure, but the existence of nano-particleschanged the preferentially growth orientation of grain. Thus, nano-particles influenced thedeposition process, which results in the refinement of grain size.The micro-hardness of composite coatings was significantly raised because of theaddition of hard nano-particles.the micro-hardness reached the highest value of 720Hvwhen the consistence of n-SiC was 10g/L, and it reached the highest value of 780HVwhen the consistence of CNTs was 15g/L. whereas the hardness of composite withlubricant nano-particles was decrease, and reached the lowest value of 416HV when theconsistence of PTFE was 25g/L. However the hardness of composite with different kindsof nano-particles was decided by the character and consistence of co-depositednano-particles. The results of polarization curves showed that these nano-particles acted as inertphysical barriers to the initiation state of corrosion, so the corrosion resistance of thecomposite coatings was improved. However, while coming to the state that localizedcorrosion gone faster than the physical barriers of fewer nano-particles, the correspondingcomposite coatings corroded faster than Ni-W-Co coating.The tribo study indicated that the wear loss of composite coatings was less than thatof Ni-W-Co coating. The composite coatings with hard nano-particles, such as SiCandCNTs nano-particles, had higher surface hardness, and the ability of resisting plasticdeformation was enhanced; the composite coatings with the lubricant nano-particles, suchas PTFE nano-particles, had lower coefficient of friction. Containing both the hard andlubricant nano-particles, the composite coatings presented the most excellent wearresistance, because of the coordination effect of these two kinds of nano-particles.