The role of silica on the superiority of corrosion barrier performance and biological properties of sintered titania-silica composite coating electrophoretically deposited on 316L stainless steel

Abstract

TiO2 and TiO2–SiO2 composite coatings were electrophoretically deposited on anodized 316L stainless steel substrates and then sintered at 1100 °C. TiO2 coating showed a rutile phase composition involving a cracked surface with a wide diffusion region rich in chromium element near the substrate. While TiO2–SiO2 composite coating showed a crack-free surface with an anatase phase comprising a continuous interlayer. Formation of the dense interlayer prevented the diffusion of substrate elements toward the coating during the sintering and thus inhibited the formation of diffusion region. According to the EIS study after 1 day of immersion in PBS solution, the highest barrier performance belonged to TiO2–SiO2 composite coating where its total faradic resistance (84 MΩ cm2) was 1500 times higher than TiO2 coating and 5.6 times higher than the anodized substrate. This was related to the crack-free surface and the interlayer formed in the composite coating owing to the improving effects of silica. After 28 days of immersion, the total faradic resistance of the TiO2–SiO2 composite coating remained significantly higher (order of 106–107 Ω cm2) than TiO2 coating (∼104 Ω cm2). Furthermore, TiO2–SiO2 composite coating enhanced the apatite formation compared to TiO2 coating or anodized substrate during immersion in SBF solution.

Keywords

• Electrophoretic deposition
• Stainless steel
• TiO2 coating
• Silica
• Interlayer
• Bioactivity