Effect of Fluoride Ions on Ti6Al4V Alloy Passivation

The corrosive behavior of Ti and its alloys in fluoride media is well known. Based on electrochemical studies, this paper describes the effect of fluoride ions on the passive behavior of Ti6Al4V alloy in lactated Ringers serum. The open circuit potential of the alloy in the serum, which lies in the passive region of TiO2, shifts to more negative values as fluoride ions are added. The voltammogram obtained in the serum presents an active-passive behavior close to -0.2 V (SCE) that changes with the presence of fluoride ions, evidencing higher anodic currents. Electrochemical impedance spectroscopy plots obtained at OCP after varying immersion times in the serum display an almost capacitive behavior and the polarization resistance becomes enhanced after 7 days. With the addition of fluoride ions, the films resistance decreases, but a stable protective layer develops after 7 days of immersion time, indicating the films repair.