Electroless Ni-P-TiO₂Composite Coatings On High-strength Steel Substrate

High-strength steel is widely used because of its excellent mechanical properties. In the implementation of high-strength steel, electroless nickel composite coating can effectively improve the corrosion resistance, but also can improve the wear resistance and hardness. In this study, the nickel coating and Ni-P-TiO2composite coating were obtained by electroless plating on the surface of the high-strength steel. The effects of the bath composition, bath temperature on the deposition rate, coating composition, and quality impact were investigated. Inaddition, the effect of the concentration of Ni2+on the deposition rate of the coating was also studied. Meanwhile, the effects of bath temperature and the additive concentration of TiO2on the deposition rate, adhesion between coating and the substrate, and the surface morphology of the composite coating were investigated. The major results were obtained as following.To optimize the rate of electroless nickel coating, the pH value, the concentrations of lactic acid, succinic acid and propionic acid were selected as the number of factors to obtain the optimum technological parameters. The results show that the appropriate parameters for electroless nickel coating are, pH value of4.5, and the concentrations of lactic acid, succinic acid, and propionic acid are10mL·L-1,10g·L-1, and5mL·L-1, respectively.Under the condition of the optimum technological parameters, the deposition of electroless nickel coating was51μm·h-1and the bright, clean, compact structure, no holes, spots, peeling and delamination defects coating was obtained. Meanwhile, the adhesion between the coating and the substrate was well. The hydrogen embrittlement of the coating was complying with the relevant requirements of the standard.The composite coating of Ni-P-TiO2was obtained on the surface of high-strength steel. The results show that the coating was composed with nickel coating and Ni-P-TiO2. The distribution of TiO2displays dispersion and inhomogeneous on the composite coating and the TiO2was growth along with the direction of the composite.On the case of a given concentration of TiO2in the electroless bath, the deposition rate of composite coating was increased by increasing the bath temperature and the amount of pore and bore diameter of the pore were decreased. However, for a given bath temperature, the deposition rate was decreased with the increasing of TiO2additive amount. Inaddition, the amount of pore and bore diameter of the pore were increased observably by increasing of TiO2additive amount.