Synthesis of Ni-P / Graphite Composite Coatings by Two Step Method of Aqueous Electrophoretic Deposition and Electroless Plating

Using the two-step method of aqueous electrophoretic deposition and electroless plating, Ni-P / graphite composite coatings were prepared. During the first step, graphite particles were deposited on a Ni-coated copper substrate from an aqueous suspension containing graphite particles and benzyl dimethyl tetradecyl ammonium chloride（BDTA）as a cationic surfactant using the electrophoretic deposition process. The deposition weight and the electric current flow depended on the concentrations of graphite particles and BDTA in the bath, the applied voltage, and the deposition time. During the second step, electroless deposition of Ni-P was performed. After the Ni-P deposition began from the surface of the substrate, it filled the pores of the porous graphite film. Through these two steps, a composite coating with graphite content of 25.4 wt% and a surface exposure area ratio of graphite particles in Ni-P matrix of 41.0% was obtained. High-temperature and high-humidity resistances of Ni-P coating and Ni-P / graphite composite coating were investigated using a pressure cooker test（PCT）conducted at 150 ℃ and 98% RH for 240 hr. The electrical resistance of Ni-P coating increased drastically, whereas that of the Ni-P / graphite composite coating showed little change after the PCT.