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
$^circhboxC$
) and the process temperature from 400
$^circhboxC$
to 800
$^circhboxC$
$(t = 60 hboxmin)$
. Nanoindentation measurements of the PIII-treated samples at 800
$^circhboxC$
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
$(3 times 10^-7 hboxAcdothboxcm^-2)$
was obtained for a PIII-treated sample during 30 min at higher temperature (800
$^circhboxC$
). 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,
$hboxTi_2hboxN$
and
$hboxTiO_2$
phases were also detected.