Characteristics investigation of Ni-diamond composite electrodeposition

Abstract

Parameters of stirring rate and temperature were designed based on electrochemical testings of cathodic polarization, electrochemical impedance spectroscopy and defferential capacitance. At the same time electrochemical action of diamond particles in the bath was studied. Interface force per unit area between particle and cathode was calculated in order to analyse the mechanism of composite electrodeposition. And then Ni-diamond composite coatings with 1.47–15.6wt.% particle content were prepared by composite electrodeposition technique in typical Watt's bath. Resultof electrochemical measurements revealed that mass fraction of codeposited diamond particles at medium stirring rate is higher than those of high and low stirring rate. Technics experiments confirmed the foretaste well. It was proved that electrochemical testing is significant for parameter designment. It was also detected that fraction of coverage θNF which had effect on non-Faraday admittance could reflect more efficiently on particle content in coating compared with fraction of coverage θF which interfered with Faraday admittance. Interface force per unit area was found to be the key for particle to entry into coating since 3.57% particles were rooted in matrix metal at just 0.0252% coating thickness/particle size. Interim stirring designed according to interface force mechanism increased the weight percentage of diamond particles in coating. The mechenism could explain the effect of particle size on particle content in coating. Calculation results show that the interface force per unit area for Ni-diamond system was close to 3.3×103N/m2. Furthermore, composite electrodeposite process can be divided into three steps. Firstly, diamond particles adsorbing positive charges are direct transported toward cathodic surface due to stirring. Secondly, a tremendous amount of particles temporary attaching on cathode are scoured back into the bath by particles in the bath and flowing solution. A few particles root quickly in coating depending on interface pressure after formation of interface between particle and fresh nickel coating with the help of high electric field intensity of electric double layer. Finally, particles are buried slowly by fresh nickel coating.