EFFECTS OF ION-IMPLANTATION ON TI-6AL-4V ON ITS FRICTIONAL BEHAVIOR AGAINST UHMWPE

The aim of this work was to study the effect of carbon ion implantatio n and a DLC coating on the friction response of Ti-6Al-4V/UHMWPE mater ials used for biomedical implants, and on the endurance of the protect ive oxide layer of the Ti alloy at increasing loads. Carbon implantati on was carried out at doses ranging from 2 x 10(17) to 10 x 10(17) ion s cm(-2) and energies from 75 to 180 keV. This implantation procedure produced a more than twofold improvement in hardness, as evaluated by a dynamic micro-indentation technique at increasing loads from 0.4 to 10 mN. Dry pin-on-disc tribological tests, using an UHMWPE pin, showed that some of the implantation treatments effectively protected the su rface of the Ti alloy, without producing a break in the protective pas sive oxide layer and exhibited low friction values, similar to those o btained in DLC coatings. No direct correlation has been found, however , between the hardening induced by ion implantation and the improved t ribological response. Formation of TiC precipitates could account for the hardening effect observed after carbon implantation and, in additi on, implantation may cause stabilisation of the protective oxide layer on the titanium surface.