Study Of Preparation And Performance Of Ni-diamond Composite Coating

With rapid development of technology and modern industry, single metal coating already can’t meet the increasing demand of material properties, so the research and application of multifunctional composite coating are more widely. Ni-based composite coating is one of the earliest and the leading resistant coating. Nickel itself is good wear resistance matrix. The diamond particles are added to nickel plating bath to prepare Ni-diamond composite coating possessing better excellent using properties. The diamond particles are incorporated into the Ni matrix and homogeneously distributed throughout the nickel matrix. The Ni-diamond composite coating, whose performance such as hardness, wear resistance and corrosion resistance has been further improved, has a broad application and receives more and more attention.Base On some problem such as bad adherence between Chemical coating and aluminum matrix, poor wetting property of water solution and diamond particle and bad suspending index, uneven distribution and low content of diamond particle in the coating, in this paper, we mainly study electroless preplating on the aluminium matrix, the treatment of diamond particles surface, selecting suitable surfactant, especially, the preparation of nickel-diamond composite coating. The main results and conclusions of this study were described as follows:(1) The effect of the reductant, complexing agent, pH value, temperature, plating time on chemical deposit adhesion were investigated, and suitable process parameters have been gotten.(2) The effect of treatment temperature, treatment time and mixed acid ratio on strong oxidation treatment effects of diamond particles surface, and the chemical scattered method is adopted to get dispersing agent A which makes diamond particles good suspend.(3) Effects of diamond concentration, dispersant content, current density, stirring speed, plating time, temperature, pH value and ultrasonic frequency on the performance of Ni-diamond composite coatings were studied by single-factor experiments, and the process condition was optimized by orthonormal experiments. The Ni-diamond composite coatings obtained under the optimum process condition have smooth and compact surface, the coating thickness and microhardness are reach to16.18μm and1927HV, respectively. The results of SEM and EDS indicate that diamond particles are equably distributed and there is no large reunite in the coatings. Mass fractions of the main element in the coating are as follows:Ni35.21%, O1.21%and C63.58%. So, the ultrafine diamond particles are successfully incorporated in the Ni matrix.(4) Analysis of XRD demonstrates that structure of Ni-diamond composite coatings is amorphous. The combining power test shows that Ni-diamond composite coatings possess good adhesion. The hardness of Ni-diamond composite coating was measured, and the result showed that the presence of diamond particles in coating greatly improves the coating hardness. Tafel plots and EIS of Ni-diamond composite coatings and pure Ni coatings demonstrate that Ni-diamond composite coatings have much better corrosion resistance than pure Ni coatings in acid, alkaline corrosive medium as well as in neutral corrosive medium.(5) Analyses of cathodic polarization curves show that the additions of complexing agent, brightener and dispersant to the plating bath cause the reduction potential of nickel to shift to more negatives, leed to decreases in the cathodic current and increase the cathodic polarization. What’s more, the slope of the reduction curve decreases, which is useful for refining grains of the coatings and brightening the coatings. The additions of wetting agent and diamond particles to the plating bath also can increase the cathodic polarization, accelerate the electrodeposition reaction, but the effect of that on nickel deposition than the first three. The electrochemical impedance spectroscopy and impedance-potential curves in the electrolyte with and without micro-diamond particles indicate that the presence of micro-diamond particles in the plating bath increase in resistance.