High temperature oxidation behavior and anti-oxidation mechanism of Ti50Al anodized in ionic liquid

• Al enriched and fluoride-containing film was prepared by anodizing in ionic liquid.
• Aluminum fluoride was oxidized to form an Al2O3 layer due to the halogen effect.
• The oxidation rate of the Ti50Al at 1000 °C was reduced by anodization.

An aluminum and fluorine enriched anodic film was fabricated on Ti50Al by anodizing in ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6). The formation mechanism and the exact role of fluorine for the generation of this anodic film were deeply investigated. Results show that the trace amounts of residual water in the ionic liquid were responsible for the generation of oxygen contained anodic film. And the formation of this aluminum enriched structure is the result of the different solubility of titanium fluoride and aluminum fluoride during the anodization in the ionic liquid. X-ray photoelectron spectroscopy analysis shows that the aluminum fluoride can be oxidized to protective Al2O3 layer at temperature higher than 300 °C. This transported Al2O3 layer together with the previously formed Al2O3 during anodization can efficiently inhibit the outward diffusion of Al and inward diffusion of oxygen, therefore improve the high temperature oxidation resistance of the Ti50Al. Upon 100 h oxidation at 1000 °C, no cracks and spallation are observed on the anodized Ti50Al.