The effect of pH on the morphology and polarization resistance of Ni-P-TiO2-ZrO2 composite coating

Nickel field composite coatings have a high ability to improve surface properties, such as increased corrosion resistance and abrasion resistance. In this study, Ni-P-TiO2-ZrO2 composite coating on AISI 316L steel substrate was deposited by direct current flow method and the effects of different pH 3, 3.5, 4 and 4.5 on coating morphology and corrosion resistance were investigated. Scanning electron microscopy (SEM) was used to investigate the microstructure. In order to investigate the corrosion behavior of the coatings, a potentiodynamic polarization test was used in 3.5% NaCl solution. The results of SEM and EDX analysis showed that the coating produced at pH = 4 had the highest uniformity and the highest amount of titanium oxide and zirconium oxide particles was related to this pH. Also, the polarization results showed that the highest corrosion resistance is related to the precipitation produced in pH = 4. At low pH and more than pH=4, the coating was not continuous and in some parts of the coating crack and pit were observed.