Effect of high-energy implantation on TAFe titanium alloy

Implantation of non-metallic ions in transition metals such as titanium typically forms high-melting phases at low temperatures. In this work, we study the effect of N+ implantation into a specific titanium alloy (Ti–5 wt.% Al–2.5 wt.% Fe) recently used for orthopedic prostheses. High-dose (1018 at cm−2) nitrogen implantation at 1 MeV was performed. Specimens were held at a constant temperature (Timp=−30 °C) and the current density was fixed at 1.5 μA cm−2 to avoid heating and fast diffusion processes during treatment. Nano-indentation results show small effects on mechanical properties, especially on hardness (with ΔH/H=35%) and elastic modulus (with ΔE/E less than 10%). Grazing incidence X-ray diffraction results indicate the formation of titanium nitrides TiN0.3. Samples have been annealed for 1 and 3 h at different temperatures in an argon atmosphere to enhance the nitriding process. At low temperature (350 °C) no evolution of hardness profiles are observed. However, at high temperature (500 °C), a significant increase of the hardness in the near surface region (H=12 GPa) and at a specific indentation depth (H=8.5 GPa) are detected. These variations are respectively correlated with the formation of a thin oxide film (TiO2) and a layer composed of a mixture of titanium nitrides (TiN+Ti2N) around the ion range. This study shows that the implanted sample can be divided into different layers corresponding to different nitride species as a function of nitrogen concentration distribution.