Titanium and titanium alloys, specially Ti-6Al-4V, are used for various medical applications, e.g. endoprosthesis. There is evidence that metallic dissolution into surrounding tissue can cause complications with the implant and the environment. Conditions such as metallosis and inflammation have been associated to the migration of metallic ions into the tissue. An explanation for this behavior was attributed to the radical transfer reaction of free oxygen in the biological system. Thus the reduction of metallic dissolution should be considered in designing new titanium alloys. A possible replacement for the Ti-6Al-4V alloys are Ti-Nb alloys.

In order to verify the influence of the radical reaction by free oxygen electrochemical tests of Ti-45wt.%Nb and Ti-35wt.%Zr-10wt.%Nb were conducted in phosphate-buffered saline (PBS) solution without and with H₂O₂ by means of potentiodynamic polarization (DC) and electrochemical impedance spectroscopy (AC). The influence of corrosion on the surface topography was studied by X-ray diffraction, SEM, TEM and Auger spectroscopy. Electrochemical measurements indicate an expanded passive region with low passive current of the investigated Ti-Nb alloys due to the formation of protective oxide films in both solutions. DC and AC measurements showed a strong influence of OH°-radicals on the passive current and the passivation mechanisms. The results obtained by electrochemical measurements will be correlated with microstructural investigations. For example, a three layer model of film formation is assumed for Ti-45wt.%Nb in PBS with radicals. Modelling as well as microstructural investigation indicate the formation of an electrochemical bilayer (Helmholtz layer), a thin inner layer and a porous outer layer.