Effect of current density on the microstructure and polarization resistance of Ni-P-TiO2-ZrO2 composite coating

Composite coatings with nickel matrix and ceramic reinforcement particles have high ability to improve surface properties, such as good corrosion and abrasion resistance. In this study, Ni-P composite coating was coated with ZrO2 and TiO2 ceramic particles on the AISI 316 steel substrate through direct current plating method. The effect of the current densities of 20, 30, 40 and 50 mA/cm2 on the microstructure and corrosion resistance was investigated. Scanning electron microscopy (SEM) was used to investigate the microstructure. In order to investigate the corrosion behavior of the coatings, potentiodynamic polarization test was used in aqueous NaCl solution of 3.5%. The results of SEM and EDX analysis showed that the coating produced at current density of 40 mA/cm2 was more uniform and had more deposition of titanium oxide and zirconium oxide particles. Also, the polarization results showed that the corrosion resistance of the coated specimen in the current density of 40 mA/cm2 (Rp = 12.3030 MΩ) was higher than that of the coated in current density of 20 (Rp = 12.1950 KΩ), 30 (Rp = 22.2710KΩ) and 50 mA/cm2 (Rp = 8.34020 KΩ). In the higher or less current densities, the coatings were not uniform.