Research On Preparation And Fractal Characterization Of Surface Topography Of Ni-based Composite Coatings With Nano-si0₂as Dispersion Phase

Nanocomposite coating is one of the effective methods for improving the surfaceproperties of material. Nano-SiO₂particles not only have the same physicochemicalproperties with conventional nano-particles, but also have high hardness and frictionresistance and other performance, what’s more, it’s cheap, as a result, the performance of thecoating will achieve a great improvement since nano-SiO₂particles is added into the coating.As we know, the surface properties depends on the quality of surface treatment and surfacemorphology, the size and content of particle added in solution, the process parameters ofplating and the surface morphology of coating will affect the quality and performance coatinglargely, but so far, the research and application in nano-composite coating has just started，thecharacterization of the coating morphology is limited to the qualitative and semiquantitative.Therefore, it is very important to find out the optimum process parameters of nano-compositcoating and acchive the quantitative characterization of surface morphology.In this thesis, nano-SiO₂uniformly dispersed by ultrasonic agitation, then Ni-SiO₂nanocomposite coatings were prepared by composite electrodeposition. The effect of the mainparameters on the preparation of Ni-SiO₂nanocomposite coatings was researched andanalysed; The technological parameters of Ni-SiO₂nanocomposite coatings prepared bycomposite electrodeposition were optimized with the L16（45） orthogonal test; theprojectivecovering method was used to calculate the fractal dimension of the coating morphology, andexplore the relationship of the surface fractal dimension of nano-SiO₂nanocomposite coatingand its microhardness.Main conclusions in the thesis were as follows:â‘´The effect of of process parameters on coating properties was studied, and five mainprocess parameters were selected as factors of the orthogonal experiment finaly, they wereselected as follow: The SiO₂nanoparticles concentration （2to11g/L）, the current density （2⁵A/dm2）, the pH value of bath （3-6）, the main salt content （200³20g/L）, the surfactant content（60¹20mg/L）;⑵Coating quality, SiO₂volume in composite coating and microhardness of coating wereviewed as the investigated factors of orthogonal experiment. The optimum process parametersof Ni-SiO₂nanocomposite coatings which were prepared by composite electrodeposition areas follow: the SiO₂nanoparticles concentration5g/L, the current density4A/dm2, the pHvalue of bath3, the main salt content240g/L, the surfactant content100mg/L;⑶Studies had shown that:The grain structure of nanocomposite coating render the multiphase structure, what is more, the coating surface is relatively flat and smooth, all ofthese due to the unique physical and chemical properties of nanoparticles. As a result, theperformance of nanocomposite coating is superior to the micron composite coating;â‘·The fractal dimension of nanocomposite coatings was calculated by the projectivecovering method. Result showed that the fractal dimension value of nanocomposite coatingsis from2.7to2.9and the correlation coefficients of linear regression are above0.98, all ofthese prove that the composite coating has obvious fractal characteristics;⑸There is a negative correlation between fractal dimension of the surface morphologyof Ni–SiO₂composite coating and its microhardness, provide a new idea and method for theresearch work on fractal morphology and performance of coating.