Ti and its alloys, for instance Ti-6Al-4V, are generally highly corrosion resistant, due to very stable passivity in various environments. These materials are widely used in biomedical applications for permanent implants, and they have an excellent reputation for biocompatibility. Some problems related to the corrosion resistance of Ti-based implants can be encountered in practical applications, mainly due to the conjoint action of chemical and mechanical attack, i.e. fretting corrosion. This can lead to release and accumulation of Ti (and alloying elements) in tissue adjacent to titanium implants. However, it is also known that depassivation of Ti can take place under deaerated acidic conditions. Even though the typical chemistry in a "bulk" biological environment is pH-neutral (buffered to pH 7.4), under certain conditions more aggressive environments can be present. Local acidification, for instance in crevices, could take place by metal cation hydrolysis reactions, but also by possible inflammation reactions (such as following a surgery). Biological reactions can also generate H₂O₂, possibly accelerating dissolution of Ti based materials.

This presentation will discuss the corrosion behavior of Ti and selected Ti alloys under different conditions, such as in deaerated acidic solutions, simulated biological environments (including slightly acidified and H₂O₂-containing solutions). Deactivation can take place in deaerated acidic solutions, especially for Al-containing Ti alloys. Electrochemical measurements and metal release studies indicate drastically increased dissolution rates in presence of H₂O₂. For Ti-6Al-4V alloy, selective phase etching is observed in H₂O₂-containing solutions.