Time Evolution of the Passivation Behavior of Ti-6Al-4V in 0.5 M Sulfuric Acid

The passivation behavior of Ti-6Al-4V alloy was studied by electrochemical and surface analyses, and a model was proposed to elucidate the connection between polarization time and properties of the passive film. Three stages of passive film growth can be divided based on the changes of current density during the formation process of passive film and the passive film grew and stabilized after polarized for 0 ∼ 2000 s under 1.0 V vs Ag/AgCl in 0.5 M H2SO4 solution. The chemical state of Ti at the topmost surface of passive film was independent of the polarization time, while the formation of oxides inside the passive film was promoted. The structure evolution of passive film was investigated by high-resolution XAS through the synchrotron radiation source. The formation and increase of thermodynamically stable rutile-TiO2 contributed to the enhancement of the impedance and corrosion resistance of passive film.