Tribological behaviour of alumina sliding against Ti6Al4V in unlubricated contact

Tribological behaviour of alumina balls (99.5%) sliding against a Ti6Al4V disc over a range of loads (5-80 N) and speeds (0.0625-1 m s^-1) has been investigated using a pin-on-disc tribometer under unlubricated conditions. The maximum wear coefficient was observed to be several orders of magnitude higher than the reported value for alumina against alumina or alumina against steel counterfaces. When the load or speed increased, the wear rate of the alumina ball increased initially and then decreased, showing typical transition features. On the other hand, the friction coefficients for the Ti6Al4V/alumina tribosystem were found to increase inversely with the applied loads or the sliding speeds. The wear mechanisms and the wear transition were investigated based on examinations of worn surfaces as well as debris using SEM, XRD and XPS, and it was revealed that a tribochemical mechanism accounted for the observed high wear rate of alumina sliding against the titanium alloy.