Polarization Behaviors of Titanium Co-Implanted with Tantalum and Nickel Ions

Abstract

Electrochemical behavior of titanium implanted with nickel, tantalum or a combination of the two has been investigated in a sulfuric acid solution, as a fuction of fluences. The metallographically polished titanium surfaces were exposed to nickel or tantalum ion beam at fluences ranging between 1×10¹⁶ and 1×10¹⁷ions/cm². The depth profiles of the implanted ion species in the near-surface regions were determined by Auger electron spectroscopy with sequential Ar bombardment. The structural change in the implanted layer was also examined by transmission electron microscopy. Polarization behavior for the implanted specimens was potentiodynamically measured in a boiling 10wt.% sulfuric acid solution.
Electrochemical measurements revealed that nickel implantation significantly promoted the passivation of titanium with an increase of fluences, and that the corrosion potentials resided in the passive region of titanium at fluences above 1×10¹⁸ions/cm². The transmission electron diffraction patterns suggested that the precipitation of Ti₂Ni occurred in the nickel implanted layer. Tantalum implantation, which caused the formation of β-phase titanium, was effective in reducing the critical current densities for passivation and passive current densities with an increase of fluences. These effects were not observed at fluences above 7×10¹⁶ions/cm². At such fluences, the concentration of the implanted tantalum was decreased by the self-sputtering effect. On the other hand, the polarization curves for combined implantation with tantalum and nickel ions exhibited stable passivation behavior with low passive current densities. It was concluded that excellent corrosion resistance of titanium in a sulfuric acid solution can be achieved by the complementary effects of the co-implantation with tantalum and nickel ions.