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. •A tribofilm was formed on Ti–6Al–4V when sliding against DLC coating.•Tribofilm was tested by nano-indentation and micro-pillar compression.•Hardness, elasticity and yield strength of tribofilm were greater than Ti–6Al–4V.•Pillar compression obtains more accurate hardness values than nano-indentation.