On the stability of passivity of Ti-Al alloys in acidic environment

The stability of passive films oil titanium and Ti-Al alloys (Ti-6Al-4V, Ti-6Al-7Nb implant alloys and Ti-50Al intermetallic compound) were studied in 0.5M H2SO4 electrolyte. Upon exposure to the acidic solution, fast open-circuit activation of native passive films on Ti-Al-V, Ti-Al-Nb and Ti-50Al takes place, whereas pure Ti remains in the passive state. Passivation in an acidic solution leads to a higher protectiveness of the passive films, as well as to a higher stability against open-circuit activation. Surface analytical experiments suggest that the stability of the passive films is related to the amount of oxidized Al in the film. No sites of high-Al content on the surface could be detected after active dissolution, which may indirectly indicate that selective dissolution of Al takes place out of the higher-Al containing phases.