Chemical composition optimization of Al2O3-TiO2 composite coatings for enhanced wear and corrosion resistance

Abstract

This study aimed to optimize the chemical composition of wear- and corrosion-resistant Al2O3-TiO2 composite coatings. 2-layered and 4-layered Al2O3-TiO2 coatings were fabricated on a 316L substrate with various Al2O3 and TiO2 content (20 %, 35 %, 50 %, 65 %, and 80 % in weight) at 900 °C by sol-gel technique. Wear properties were measured by dry sliding tests against an Al2O3 ball, and corrosion behavior was determined through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. All Al2O3-TiO2 composite coatings consisted of α-Al2O3 and rutile phases, regardless of the chemical composition. Increasing TiO2 content significantly increased coating thickness at the same number of layers. The 2-layered configurations resulted in lower wear rates in low-TiO2 compositions, whereas the 4-layered configurations provided higher wear resistance in high TiO2-containing coatings. The high Al2O3 concentration caused extremely high corrosion rates compared to those consisting of high TiO2. Wear and corrosion losses were decreased with increasing TiO2 content due to its nanosized structure, allowing well-adhered, continuous, and less porous coating morphology. The maximum improvement in wear and corrosion resistance was obtained in the 4-layered 65 % TiO2-containing composite coating.