Electrochemical evaluation of Ti-13Nb-13Zr, Ti-6Al-4V and Ti-6Al-7Nb alloys for biomedical application by long-term immersion tests

In this investigation the electrochemical behaviour of the Ti13Nb-13Zr, Ti-6Al-4V and Ti-6Al-7Nb alloys, for application as implant materials was evaluated in Hanks' solution by electrochemical techniques. The alloys were immersed in this solution for 410 days and periodically they were tested by electrochemical impedance spectroscopy. At the end of this period, polarization curves of the three titanium alloys were obtained. The electrochemical impedance experimental results were interpreted using an equivalent electrical circuit that simulates a duplex structure oxide composed of an inner compact layer, here called barrier layer, and an outer and porous layer. The results indicated that all the alloys present a very high corrosion resistance in the electrolyte used, typical of passive alloys, and that the corrosion resistance is mainly due to the barrier layer. The passive like behaviour was maintained during the whole period of test.