It was noted that the out-diffusion of toxic Ni ions from NiTi (Nitinol), often used for biomedical applications, could be strongly reduced by using oxygen plasma immersion ion implantation. Non-radioactive isotope markers, 60Ni and 46Ti, were implanted at 180keV into NiTi prior to the oxygen implantation to fluences of between 0.4 x 1016 and 4 x 1016at/cm2. Implanting oxygen ions by plasma immersion ion implantation at 400 to 550C led to a surface oxide layer consisting of pure TiO2. The results proved that Ni cations were the mobile species, while Ti was immobile during the oxygen insertion.

Marker Experiments to Determine Diffusing Species and Diffusion Path in Medical Nitinol Alloys. J.Lutz, J.K.N.Lindner, S.Mändl: Applied Surface Science, 2008, 255[4], 1107-9