Effects of ion implantation on Ti-6Al-4V on its frictional behaviour against UHMWPE

The aim of this work was to study the effect of carbon ion implantation and a DLC coating on the friction response of Ti-6Al-4V/UHMWPE materials used for biomedical implants, and on the endurance of the protective oxide layer of the Ti alloy at increasing loads. Carbon implantation was carried out at doses ranging from 2 x 10(17) to 10 x 10(17) ions 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 surface of the Ti alloy, without producing a break in the protective passive oxide layer and exhibited low friction values, similar to those obtained in DLC coatings. No direct correlation has been found, however, between the hardening induced by ion implantation and the improved tribological response. Formation of TiC precipitates could account for the hardening effect observed after carbon implantation and, in addition, implantation may cause stabilisation of the protective oxide layer on the titanium surface.