Effects of the High-Temperature Plasma Immersion Ion-Implantation Treatment on Corrosion Behavior of Ti-6Al-4V

Nitrogen implantation into Ti alloys at higher temperatures improves their mechanical and corrosion resistance properties by forming a thicker nitride layer. In this paper, two different sets of Ti-6Al-4V samples were plasma immersion ion implantation (PIII)-treated using nitrogen plasma, varying the treatment time from 30 to 150 min (800 degC) and the process temperature from 400 degC to 800 degC (t=60 min). Nanoindentation measurements of the PIII-treated samples at 800 degC during 150 min showed the highest hardness value, 24 GPa, which is about four times bigger than untreated sample hardness. The N penetration at these conditions reached approximately 150 nm as analyzed by Auger spectroscopy. On the other hand, the lowest passive current density (3times10^-7 Amiddotcm^-2) was obtained for a PIII-treated sample during 30 min at higher temperature (800 degC). The corrosion resistance of this sample is almost the same as for the untreated specimen. Corrosion behavior evidenced that in strong oxidizing media, all PIII-treated samples are more corrosion resistant than the untreated one. PIII processing at higher temperatures promotes smoothing of the sample surface as observed by scanning electron microscopy (SEM). Grazing incidence X-ray diffraction analyses of the untreated samples identified the two typical Ti phases, Ti alpha and Ti beta. After the implantation, Ti₂N and TiO₂ phases were also detected