Investigation on mechanical properties of tribofilm formed on Ti-6Al-4V surface sliding against a DLC coating by nano-indentation and micro-pillar compression techniques

A tribofilm was formed on the Ti-6Al-4V surface when sliding against a DLC coating under fretting condition in air. The tribofilm is mainly composed of the oxidized wear product of Ti-6Al-4V alloy. The mechanical properties of the tribofilm and the Ti-6Al-4V alloy were characterized using nano-indentation and micro-pillar compression techniques. From nano-indentation testing, the hardness of tribofilm (10 +/- 0.4 GPa) was 2.6 times higher than that of Ti-6Al-4V alloy (3.9 +/- 1.5 GPa). The reduced Young's modulus of tribofilm (170 +/- 3 GPa) was around 1.3 times higher than that of Ti-6Al-4V alloy (130 +/- 30 GPa). From micro-pillar compression testing, the compression modulus of tribofilm (around 160 GPa) was 2.5-3.3 times higher than that of Ti-6Al-4V alloy (47-62 GPa). The yield strength of tribofilm (around 6.4 GPa) measured by micro-pillar compression, was 6.7-7.1 times higher than that of Ti-6Al-4V alloy (0.90-0.95 GPa). When measuring the hardness on the tribofilm, micro-pillar compression tests could obtain more accurate values than the nano-indentation tests.