Tribological Behaviour of Plasma-Spray TiO2 Coating against Metallic Bearing Materials Under Oil Lubrication

Abstract

In this work, a block-on-ring test rig has been used to investigate the tribological behaviour of plasma-spray TiO2 coating pairing with conventional metallic bearing materials; and the effect of triphenyl thiophosphate (T451) and tricresyl phosphate (T306 or TCP) on tribological behaviour of TiO2 coating/AISI 1045 steel was also studied. Test results indicated that the copper—lead alloy paired with TiO2 coating under the base oil exhibited the optimum tribological performance, scanning electron microscope (SEM) analysis of worn surface of the steel block indicated that the wear mechanism was dominated by abrasion and corrosion. Either T451 or T306 alone can improve the tribological behaviour of TiO2 coating/AISI 1045, and T451 with the same percentage was more efficacious than T306 in reducing the friction coefficient and wear rate. Basically, as the ratio of T451 to T306 is greater than 1:1, the better synergistic effect in friction-reduction property can be obtained. Within the limit of the experimental data acquired, base oil containing 2 wt%T451+1 wt%T306 led to the significant synergistic effect of friction reduction and antiwear property for the TiO2/AISI 1045. SEM images showed that wear mechanism of the worn surfaces of the steel blocks were the slight plowed grooves and corrosion pits. Meanwhile, the atom concentrations of the elements S and P on the steel specimens worn surfaces were too low to be referred for analysing the tribo-chemical reaction mechanism.