Effect of Ni–P and Phosphate Intermediate Layers on Al2O3 Coating Developed by Sol-Gel Method

Abstract

Sol–gel method was used for applying of alumina coating on carbon steel substrate. Alumina sol was prepared with Al-isopropoxide as a precursor material. Specimens were coated with prepared alumina sol by dip coating technique. Either a film of Ni–P or phosphated intermediate layer has been pre-deposited on the carbon steel substrate by electroless plating to improve the adherence of alumina coating. The corrosion resistance of coatings in the presence of intermediate layers was evaluated by electrochemical measurement in 3.5% NaCl solution by open-circuit potential measurement at room temperature. The abrasive wear behavior of sol–gel coated specimens was measured in high stress conditions. The results indicate that, after applying an intermediate layer of phosphate or Ni–P by electroless plating technique, the wear and corrosion resistance of alumina coating have been improved. Moreover, the phosphate intermediate layer has been associated with a higher corrosion resistance, while the intermediate layer of Ni–P is more effective to improve the hardness and wear resistance of alumina coating.