Alumina/metal tribopairs: Which is the wearing element under tribocorrosion conditions?

Alumina wears when rubbing against certain metals (titanium and its alloys, nickel or ruthenium among others) in water lubricated contacts. However, alumina does not wear under similar tribocorrosion conditions (combined action of wear and corrosion) when sliding against metals and alloys such as CoCr alloys, stainless steels and tungsten. In this paper, we aim at understanding the physicochemical phenomena occurring at the interface ceramic/metal responsible for the alumina degradation. For this, a literature review and an experimental series of tribocorrosion tests of alumina balls sliding against nickel and a titanium alloy in a unidirectional tribometer coupled to an electrochemical cell was carried out. The influence of the metal surface chemistry on the wear of alumina was analyzed by changing the electrochemical conditions. The combination of the obtained experimental results and those reported in literature show that alumina wears when aliovalent ions (with valence different to 3) from the metallic counterpart are generated within the tribological contact.