Marine microbial corrosion inhibitation of an in situ formed oxide coating on Ti56Zr44 alloy

Abstract

The microbiologically influenced corrosion causes serious harm to the titanium alloys used for marine engineering. It is of great significance to explore the methods to prevent the microbial corrosion of titanium alloy. In this work, an in situ formed ZrTiO4 coating was prepared on Ti56Zr44 (at. %) alloy by thermal oxidation treatment at 450 °C. The biofilm formation on Ti56Zr44 alloy with and without oxide coating was comparatively investigated by immersion experiments in 2216E culture medium containing Pseudomonas aeruginosa bacteria. The microbial corrosion behavior of Ti56Zr44 alloy was evaluated by electrochemical methods. The results show that Ti56Zr44 alloy displays pitting corrosion when immersing for 10 days. The maximum pitting depth is up to 3.7 μm after 30 days of immersion. The pitting corrosion is attributed to that oxygen poor environment under biofilm causes the transfer of bacteria extracellular electron to the passive film. TiO2 in passive film is reduced to Ti2O3, decreasing the stability of passive film. The synergistic action of the biofilm and chloride ions in medium solution leads to pitting corrosion. On the contrary, no pitting corrosion occurs on the coating surface in spite of the coverage with biofilm. The corrosion rate of the Ti56Zr44 alloy with oxide coating is decreased by nearly five times when immersing for 30 days. The improved chemical stability of the coated alloy result from that there are more covalent bonds and hydrogen bond receptors in lattice unit cell of ZrTiO4 than that of TiO2 or ZrO2. It is difficult for the stable chemical structure to accept extra electrons provided by bacteria and change its own valence. The good resistance of the oxide coating to microbiological corrosion increases the application potential of Ti56Zr44 alloy in marine engineering.