Au-Ni-TiO₂Nano-Composite Coatings Prepared by Sol-Enhanced Method

Abstract

Gold coatings are widely used in many fields for their shining color, excellent corrosion resistance, and electrical conductivity. However, they are not mechanically strong with low wear resistance. In this paper, we have prepared nano-composite Au-Ni-TiO 2 coatings by our newly developed sol-enhanced electroplating method. In order to obtain the optimal mechanical properties, a systematic study of Au-Ni-x TiO 2 coatings with different sol concentrations (x is the sol doping concentration from 0 to 25 mmol/L) has been conducted. It was found that nano-particles (3-12 nm) of TiO 2 were highly dispersed in the coating matrix. The mechanical properties of sol-enhanced nano-composite coating were significantly increased. The nano-hardness of the coatings was improved from 2.55 ± 0.13 GPa to 3.20 ± 0.15 GPa. Consequently, the scratch resistance and wear resistance of the sol-enhanced coating were also improved significantly. Meanwhile, the electrical resistivity of the sol-enhanced coatings keeps a same level as the pure Au-Ni coatings. Gold (Au) and gold alloy have been widely used in various applications for their unique properties such as beautiful/shining color, high chemical stability, good ductility, excellent conductivity, and good weldability.1-5 Au, Au alloy and Au based composite coatings have been synthesized by various technologies, such as E-Beam Evaporation, Magnetron Sputtering, Sol-gel deposition, Chemical Vapour Deposition (CVD), Electrochemical Over-potential Deposition (OPD), and Electroplating.6-9 Among these fabrication methods, electroplating method is a simple way to fabricate gold coatings because of its energy effectiveness, time efficiency, without using vacuum technology and the controllability of coating thickness and grain size. 10In order to improve the hardness of pure Au, alloy elements such as Co and Ni were co-deposited with Au, which is known as hard Au. Hard Au can be used on decoration surface and electrical components where shining color, chemical inertness and good wear resistance are combined. As expected, however, the electrical conductivity decreased with increasing mechanical strength. 11,12For the requirements mentioned above, the mechanical properties such as wear resistance and hardness of coatings are the most important factors which dominate the durability and service life of coated parts. In the past decades, many attempts were devoted to improve the mechanical properties of Au coatings. One of the popular methods is using hard particles to form composite coatings. [13][14][15] It is widely accepted that the highly dispersive nano-particles in composites can realize good strengthening effect. In order to achieve good dispersion of nano-particles, the electrolyte has be to maintained by special techniques, such as vigorous agitation, air injection, and/or adding surfactants. However, it is difficult to achieve good suspension because of the small particle size and large surface energy, which caused agglomeration of the nano-particles. The surface appearance of Au based ...

Microstructure and properties of Cu-Sn-Zn-TiO2 nano-composite coatings on mild steel

“…Comparing with the Chromium (Cr) [19] or Nickel (Ni) [20,21] , which are the mostly used coating, Cu-Sn-Zn coating possesses a relatively soft hardness. In order to improve the mechanical properties and explore the application of Cu-Sn-Zn coatings, the preparation of Cu-Sn-Zn based nano-composite coatings, i.e., incorporating the second phase or other nanoparticles into coating matrix, could be a potential solution [20][21][22][23].…”

Nanocomposite Coatings Deposited by Sol-Enhanced Electrochemical Methods

“…The small particles in sol with the charge on the surface cannot grow up for the covered layer of solvent molecules. Different small particles can be well suspended in the solvent, subjecting to the combined effect of charge, van der Walls force and gravity [9][10][12][13]. The hydrolysis reaction and condensation process of TiO 2 sol has been widely investigated.…”

“…As abundant TiO 2 nano-particles agglomerate into clusters, porous structure formed in the nearby area. The other black dots are the voids that may come from the H 2 release during the electro-deposition process [12][13]. Fig.…”

“…When proper TiO 2 sol was added into electrolyte, a good dispersion strengthening and grain refinement can be achieved, resulting in a significant improvement of mechanical property for the coating. However, when excessive TiO 2 sol was added into electrolyte, TiO 2 nanoparticles start to agglomerate and tend to cause porous structure in the grain boundaries, which reduced the effect of dispersion strengthening; finally lead to a deterioration of the mechanical property although the grain size was continuously decreased [12][13].…”

“…The slight decrease of electrical conductivity can be attributed to the increment of scattering effect. The increase of grain boundaries and the scattering effect of electron wave strengthened by the second phase lead to the decrease of electrical conductivity [13].…”