Implantation of N-2(+), O+ and CO+ ions into titanium and Ti-6Al-4V

The marginal wear resistance of titanium-based alloys is known to increase significantly when hard compounds are formed at the surface. In particular the ion implantation technique has proved to be successful when polished surfaces have to be treated without modifications to the surface roughness. Therefore polished titanium and titanium alloys were implanted with high doses of N-2(+), O+ and CO+ ions up to an energy of 200 keV. The ion beam was generated by running the ion source with either nitrogen or carbon dioxide. The fragmentation of the molecular gases was investigated by mass separation of the beam with a mass-analyzing magnet. High beam currents of molecular CO+ and atomic O+ could be extracted when the source was operated with carbon dioxide, whereas molecular N-2(-) was extracted by running the source with nitrogen. A chemical analysis of the modified surface layers, which have depths below 400 nm, was carried out using X-ray photoelectron spectroscopy (XPS). Implantation of high doses between 3 x 10(17) and 1 x 10(18) is ions cm(-2) resulted in the formation of hard wear-resistant phases, which were identified by the chemical shift in the XPS signal. The spectra revealed the formation of TiN in the case of N-2(+) implantation and the formation of TiO in the case of O+ implantation. At low concentrations of implanted CO+, the formation of Ti(C, O) was observed whereas, at high concentrations, carbon-carbon bonds were identified.