A comprehensive investigation of the tribological behaviour of α, α+β, and β titanium alloys against a steel counterpart

The tribological behaviour of three different natures of titanium alloys, the α (T50), α+β (Ti-6Al-4V) and β (Ti-5553), against a steel ball counterpart was investigated for different surface conditions produced by surface severe plastic deformation (SSPD) at room and cryogenic temperatures.

Friction led to the formation of various oxides that acted as third bodies and resulted in different wear regimes referred to as stages I, II, and III. Stage I, the initial abrasive regime under which TiO₂-anatase formed, was the only characteristic of the β Ti-5553 alloy behaviour. In addition, stages II and III were observed for the α T50 and α+β Ti-6Al-4V alloys. Stage II is characterised by an increase in the coefficient of friction (COF) associated with the formation of hard TiO₂-rutile. Stage III corresponds to the formation of Fe-oxides induced by the steel ball abrasion. While the COF remained steady during stage III for T50, the presence of β-phase in the Ti-6Al-4V destabilised periodically the Fe-oxide layer during stage III and generated repeated sharp drops in the COF values.

Despite increasing hardness and roughness of the treated surfaces, SSPD did not modify the overall mechanisms of abrasion and improved only slightly the tribological properties.