A novel electroless plating of Ni-P-TiO₂ nano-composite coatings

A new processing concept has been developed to produce nano-structured metal-matrix composite coatings. This method combines sol-gel and electroless plating techniques to prepare highly dispersive oxide nano-particle reinforced composite coatings. Transparent TiO₂ sol was added into the standard electroless plated Ni-P solution at a controlled rate to produce Ni-P-TiO₂ nano-composite coatings on Mg alloys. The coating was found to have a crystalline structure. The nano-sized TiO₂ particles (∼ 15 nm) were well dispersed into the Ni-P coating matrix during the co-deposition process. This technique can effectively avoid the agglomeration of nano-particles in the coating matrix. As a result, the microhardness of the composite coatings were significantly increased to ∼ 1025 HV₂₀₀ compared to ∼ 710 HV₂₀₀ of the conventional composite coatings produced with solid particle mixing methods. Correspondingly, the wear resistance of the new composite coatings was also greatly improved.