Study On The Preparation And Properties Of Ni-P-Nano TiO₂ Composite Coating

Nanometer-sized TiO₂ particle-reinforced nickel-phosphorus matrix composite (Ni-P-TiO₂) coatings were prepared by electroless deposition in this thesis. Influences of reductant, stabilizer, pH value and temperature on deposition rate were studied, and the effects of various surfactants, agitating, temperature and bath content of nano particles on the hardness of the coating were also investigated. Optimum formula was obtained and a smooth and compact composite coating of 30μm thick was prepared. It is found that the hardness of the composite coatings after the plating and heat treatments of various temperature was higher than that of the corresponding Ni-P alloy coatings. Chemical analysis showed that the content of TiO₂ particles was 2.14-wt%. XRD analysis showed that the structure of the composite coating changed from amorphous to crystalline after heat treatment at 200 ℃, and nickel phosphide (Ni₃P) precipitated at 400 ℃. The hardness of the composite coatings after heat treatment was as high as Hv1100. It was found that the crystallization temperature of the composite coating did not decreased. The open-circuit potentials of alloy coating and composite coating were tested in 3.5% sodium chloride...