The corrosion behaviour of Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr in protein solutions

Ti alloys are used in orthopaedic applications owing to their appropriate m echanical properties and their excellent corrosion resistance. The release of titanium and the other alloying elements into the surrounding tissue has been reported due either to passive corrosion or accelerating processes su ch as wear. Since the passive layer can be broken down in certain circumsta nces by wear it is important to study the ability of these alloys to repass ivate in biological environments, in particular in the presence of proteins , and evaluate how the repassivated surface may vary from the original surf ace. In this study we investigated the ability of Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr to repassivate in phosphate buffered saline (PBS), bovine alb umin solutions in PBS and 10% foetal calf serum in PBS at different pH valu es and at different albumin concentrations. It was found that an increase i n pH had a greater effect on the corrosion behaviour of Ti-6Al-4V and Ti-6A l-7Nb than on Ti-13Nb-13Zr in PBS and that the addition of protein to the P BS reduced the influence of pH on the corrosion behaviour of all the alloys . The effect of the corrosion and repassivation was investigated by measuri ng changes in the surface hardness of the alloys and it was found that corr osion reduced the hardness of the surface oxides of all the alloys. In PBS the reduction was smallest for Ti-6Al-4V and largest for Ti-13Nb-13Zr and t hat corrosion in protein solutions further reduced the hardness of the surf ace oxides. This effect was greater for Ti-6Al-4V and Ti-6Al-7Nb than for T i-13Nb-13Zr. In conclusion, proteins in the environment appear to interact with the repassivation process at the surface of these alloys and influence the resulting surface properties. (C) 1999 Elsevier Science Ltd. All right s reserved.