Tribocorrosion behaviour of plasma nitrided and plasma nitrided + oxidised Ti6Al4V alloy

This paper reports the influence of low pressure plasma nitriding treatments, some of them followed by plasma assisted oxidation on the mechanical properties and tribocorrosion resistance of a Ti6Al4V alloy. Nitridation was performed for 640 or 720 min at 600 and 700 °C in a r.f. plasma equipment, using a N2–H2 gas mixture at 7.5 Pa. Some of the samples were then post-oxidized at 700 °C for 15 and 60 min, within a O2 plasma of 9.5 Pa. XRD results revealed the occurrence of the Ti2N phase for the nitrided samples. The oxidized surface layers are poorly crystallised with rutile and traces of anatase TiO2 nanocrystallites. Microhardness tests showed a significant improvement of the surface hardness whatever the treatment, with a slight effect of the treatment temperature. The tribocorrosion results clearly showed that plasma treatments have a strong influence on the tribocorrosion behaviour of the material. Both the corrosion and wear performance of the samples are improved by the increase of the processing temperature.