Nanohardness, friction and wear properties of nitrogen ion implanted Ti-6Al-4V alloy

Over the last few years a large amount of evidence has appeared in literature covering the effect of ion implantation on the wear behaviour of Ti-6A1-4V alloy, a material widely used in medical and aerospace applications. Recent studies have shown improved hardness and wear properties of this alloy in as-implanted condition only, and any post-implantation annealing treatment causes a reversal of this effect. In this paper the influence of higher energy and high dose nitrogen ion implantation followed by post-implantation annealing on the microhardness, friction and wear behaviour of polycrystalline Ti-6A1-4V alloy is demonstrated. Polycrystalline Ti-6A1-4V alloy samples were implanted with 150 kev N+ ions, and the hardness, friction and wear behaviour was investigated before and after annealing at 705 deg C for 2 hours. The hardness was measured by an ultramicrohardness indentation system and wear and friction were evaluated by sliding 1.6 mm ruby ball against the discs. The results shows that the hardness increased by 150 % in as-implanted and 200 % in annealed sample, the coefficient of friction is reduced from 0.29 in virgin sample to 0.11 in as-implanted to 0.08 in annealed sample. Wear rate was reduced by 50 % in as-implanted and 67 % in annealed sample, while post-implantation annealing caused the formation of TiN phase at sub-surface of the sample. 4 refs., 3 figs