Studies On Characterization And Mechanism Of Au-based Nanocomposite Coatings Prepared By Pulse Electroplating Technology

Electroplating nanocomposite coatings have attracted considerable interest for their superior mechanical, tribological and electrical contact properties. In recent years, as a new electroplating nanocomposite technology, pulse current electroplating (PC) nanocomposite technology has been developed greatly combined with advantages of pulse electroplating technology and nanocomposite technology. However, few results have been reported on the research of pulse electroplating nanocomposite coatings at home and abroad. And the studys on the relationship between PC nanocomposite process and characterization of nanocomposite coatings are still inadequate. So, much research work should be carried out for the mature PC nanocomposite technology.In order to study the characteristic of PC nanocomposite technology and to obtain optimal mechanical properties of nanocomposite coatings, the effect of PC process on the properties and microstructures of nanocomposite coatings has been investigated.The Au-SiO₂ and Au-SiC nanocomposite coatings are prepared by PC nanocomposite technology and the nanocomposite coatings are analyzed by ESEM, EDX and XRD. Compared with direct current (DC) electroplating, the results show that PC nanocomposite technology has several advantages such as the availability of additional process parameters which can be altered independently and possibility of achieving excellent coatings, PC nanocomposite technology can receive a higher particle content in composite coatings, and the crystal grains of PC nanocomposite coatings are much finer, denser and lower porosity than DC nanocomposite coatings. The influence on SiO₂ and SiC nanoparticle content in composite coatings of the parameters of PC electroplating technology such as average cathodic current density, duty ratio and pulse period are investigated detailedly for optimal conditions.The microhardness and wear behavior of PC nanocomposite coatings have been analysed and the influence on microhardness of the parameters of PC electroplating technology such as average cathodic current density, duty ratio and pulse period have been investigated. Moreover the wear tracks of all kinds nanocomposite coatings have been analyzed by ESEM and the wear mechanisms of pure Au coatings and PC nanocomposite coatings have been discussed. The results reveal that PC nanocomposite coatings have a higher hardness and excellent wear resistant property.This wear behavior could be attributed to the reason that the effective dispersion of nanoparticles provided by PC process would significantly decrease the agglomeration of nanoparticles. The properties of microhardness and wear of Au-SiC nanocomposite coating are superior to Au-SiO2 for the difference of physical character between two nanoparticles. The corrosion behaviors of different coatings have been analyzed by anodic polarization curves for coatings in 3.5% NaCl medium, H2S gas test and artifical sweat test , The results show that pure Au coatings is superior to the other coatings on the corrosion resistance property, and PC nanocomposite coatings behave better than DC nanocomposite coatings and Au-Ni alloy coatings. Moreover, through the analysis of contact resistance of different coatings, we also find that PC nanocomposite coatings maintain excellent electrical coantct property with high wear resistance property after the nanoparticles are embedded in coatings. Based on the research on theζpotentials of SiO2 and SiC in electrolyte and the anodic polarization curves of the electrolyte after adding nanoparticles or promoting agents, the mutual interactions between the cathodic surface and nanoparticles are investigated and the mechanisms of composite electroplating are discussed.