Effect of g-family incorporation on corrosion behavior of PEO-treated titanium alloys: a review

By being exposed to air or moisture or by a chemical reaction, titanium (Ti) forms an oxide layer 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 its extremely low thickness (∼10 nm), this oxide layer is easily destroyed under corrosion conditions. Through plasma electrolytic oxidation (PEO), titanium and titanium alloys can be equipped with thick and adhesive titanium dioxide (TiO₂) coatings to enhance their surface characteristics. In the PEO process, titanium dioxide composite coatings can be formed by mixing proper additives with electrolytes, such as powders, particles, sheets or compounds. 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 electrolytes can be useful in reducing coating porosity and improving final corrosion properties by adjusting electrolyte conditions. Therefore, the diffusion pathways for corrosive ions in composite titanium dioxide coatings become considerably more tortuous than those for pure titanium dioxide.