Improved microstructure and physiochemical properties of hopeite conversion coating by Si3N4 nanoparticles doping

The effect of nano-scaled Si 3 N 4 particles on the microstructure, mechanical and electrochemical behavior of hopeite (Zn 3 (PO 4 ) 2 ·4H 2 O) conversion coating on pure titanium was investigated. Different concentrations of nanoparticles were dispersed into the phosphating bath to incorporate the process of coating deposition. The XRD results demonstrated that nano-Si 3 N 4 were doped into the coatings without any decomposition or reaction with the hopeite phase. A finer and denser microstructure of the composite coating could be obtained at the addition of 0.5 g/L Si 3 N 4 in comparison with the pure hopeite coating. Moreover, the composite coating presented a higher bonding strength and corrosion resistance related to the refinement of microstructure and filling of the embedded nanoparticles. It is suggested that the incorporation of nano-Si 3 N 4 particles in conversion coating is a promising approach for performance optimization.