Improvement of corrosion resistance of titanium by co-implantation

A number of investigations have successfully represented the beneficial effects of ion implantation in improving the corrosion resistance of metals. In this paper, we review studies on improving the corrosion resistance of titanium by co-implantation with metal ions. These studies have demonstrated that co-implantation is a possible process for attaining excellent corrosion protection of titanium against aggressive environments. The electrochemical behavior of titanium implanted with tantalum, molybdenum, nickel ions, or combinations of two of these ions, have been investigated in boiling sulfuric acid solution. The polarization curves of tantalum-implanted titanium are similar to that of unimplanted titanium, showing the active region followed by passivation. However, anodic polarization current densities are considerably decreased in the active and passive regions, and tantalum implantation suppresses the dissolution of titanium. The corrosion potentials of titanium implanted with nickel or molybdenum are shifted in the noble direction with an increase in fluence, and reside in the passive region of titanium at higher fluences. No significant change is observed in the passive current densities. Nickel and molybdenum implantation preferentially promotes the passivation of titanium in such an aggressive environment. These effects are diminished in a relatively short-term immersion. Titanium implanted with a combination of molybdenum and tantalum ions, or a combination of tantalum and nickel ions, exhibits stable passivation behavior with low passive current densities. The corrosion rate estimated from the polarization curves is approximately 0.1 mm year(-1) for co-implantation with tantalum and nickel ions. Go-implantation provides long-term protection for immersion. The outstanding corrosion resistance of titanium is achieved by the complementary effect of co-implantation with these metal ions.