Effect of graphene-family incorporation on corrosion performance of PEO coatings formed on titanium alloys: a mini review

By being exposed to air or moisture or by a chemical reaction, titanium forms an oxide layers on its surface, which is stable and tightly adherent and provides it with protection from the environment, since titanium is a reactive material. Due to their extremely low thickness (similar to 10 nm), this oxide layer is easy to destroy under corrosion conditions. Through plasma electrolytic oxidation (PEO), titanium and titanium alloys can be equipped with thick and adhesive TiO2 coatings to enhance their surface characteristics. In the PEO process, TiO2 composite coatings can be formed by mixing proper additives with electrolytes, such as powders, particles, sheets, or compounds. The graphene and its family derivatives (i.e., graphene oxide and reduced graphene oxide) are among the most popular additives used in PEO composite coatings due to their high stability in corrosive media. Graphene family nanosheets can accumulate in PEO coatings because of their porous nature, changing the surface characteristics dramatically. The use of graphene family nanosheets in the electrolyte can be useful to reduce coating porosity and improve final corrosion properties by adjusting electrolyte conditions. Therefore, the diffusion pathways for corrosive ions in composite TiO2 coatings become considerably more tortuous than with pure TiO2.