Dry sliding wear of Ti-6Al-4V alloy as influenced by the counterface and sliding conditions

The dry sliding wear behaviour of the Ti-6Al-4V alloy sliding against itself and AISI M2 steel was investigated at different sliding velocities (between 0.3 and 0.8 m/s) and applied loads (between 50 and 200 N). Two wear mechanisms were identified, irrespective of the counterface and applied load: oxidation wear at the lowest sliding velocities (0.3-0.5 m/s) and delamination wear at the highest (0.6-0.8 m/s). Wear rate was higher against the AISI M2 at the lowest sliding velocities, and it continuously decreased as sliding velocity was increased. On the other hand, as the sliding velocity was increased it first decreased, experienced a minimum and then became very severe in the case of sliding against the Ti-6Al-4V alloy. This behaviour was explained by making reference to the effect of the counterface. At the lowest sliding velocities, the AISI M2 counterface exerted an abrasive effect on the Ti-6Al-4V alloy, thus accelerating its oxidative wear. At the highest sliding velocities, metallic delamination (which developed through the formation of a mechanically mixed layer (MML) on the surface) was the controlling wear mechanism and the thermal effects connected with the frictional heating became of primary importance. Thus, as surface temperature increased (due to an increase in load or a decrease in the thermal conductivity of the counterface, i.e., in passing from the Ti-6Al-4V counterface to the AISI M2) the plastic strain rate at the contacting asperities also increased (by reversible dislocation motion) and wear rate also increased, in accordance with the theory of delamination. (C) 1999 Elsevier Science S.A. All rights reserved.