Effects of the high-temperature plasma immersion ion-implantation treatment on corrosion behavior of Ti-6A1-4V

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-6A1-4V samples were plasma immersion ion implantation (PIII)-treated using nitrogen plasma, varying the treatment time from 30 to 150 min (800 [degrees]C) and the process temperature from 400 [degrees]C to 800 [degrees]C (t = 60 min). Nanoindentation measurements of the PIII-treated samples at 800 [degrees]C 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 (3 x [10.sup.-7] A * [cm.sup.-2]) was obtained for a PIII-treated sample during 30 min at higher temperature (800 [degrees]C). 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, [Ti.sub.2]N and Ti[O.sub.2] phases were also detected. Index Terms--Corrosion, hardness measurement, ion implantation, titanium alloys.