A Study Of Preparation And Properties Of Nanocomposite Coatings

Recently, nanocomposite plating technology has received increasing attention in view of the interesting possibilities that the codeposition of the nano-particles with metal phases can bring a remarkable improvement on physical and chemical properties of the coatings. In this thesis, we have investigated the preparation and property of Ni-W/SiC nanocomposite coating, Ni-W/ZrOB2 Bnanocomposite coatings and Ni-P/WC nanocomposite coating. The addition of SiC nano-particles would lead to an increase in hardness of the Ni-W/SiC nanocomposite coatings. The co-deposited SiC nano-particles in deposit increase the wear resistance and reduce the wear weight loss. Moreover, the wear resistance of Ni–W/SiC nanocomposite coatings is closely related with SiC content in deposit. The co-deposition of SiC nano-particles in the composite coatings increased the corrosion resistance. The high temperature oxidation resistance of Ni-W alloy coating, Ni-W/ ZrOB2B nanocomposite coating and Ni-W/ ZrOB2B composite coating is analyzed．The results of thermogravimetry (TG) and differential scanning calorimetry (DSC) show that the addition of ZrOB2B nano-particles can obviously improve the oxidation resistance of the nanocomposite coatings. The hydrogen evolution reaction of Ni–W/ZrOB2B nanocomposite coatings was investigated by the polarization curves and potentiostatic curves. Arrhenius curves of Ni-W/ZrOB2B nanocomposite coating were calculated. The results indicate that the Ni–W/ZrOB2B nanocomposite coatings obtained higher electrochemical activity than Ni-W alloy coating. The hardness of Ni-P/WC nanocomposite coatings increases with the increasing content of the WC nano-particles in the coatings. The Ni-P/WC nanocomposite coating has better corrosion resistance than the Ni-P alloy coating in NaCl solution. Tribological behavior of Ni-P/WC nanocomposite coatings was investigated using a Block-on-Ring test rig; the effect of mass fraction of WC nano-particles on tribological behavior of the composite coatings was examined. The Ni-P/WC nanocomposite coatings revealed a low coefficient of friction compared with the Ni-P alloy coating. Due to the effects of the reinforcement and reduced friction, the wear rate of the nanocomposite coating decreased with increasing mass fraction of WC nano-particles. The valence of Ni, W, P, Si and Zr element in nanocomposite coatings was investigated by using XPS. The result shows that there is chemical interaction among the elements in such nanocomposite coatings. The main possibility of this phenomenon occurrence may result in the large specific surface area and large surface energy of nanoparticles, therefore, the atoms on nano-particles' surface are apt to interact with the atoms in alloy matrix and chemical shift appears. The chemical interaction between nano-particles and alloy matrix is the main causation that improves the properties of nanocomposite coatings.