Tribological behaviour of TiO2 Atmospheric Plasma Spray (APS) coating under mixed and boundary lubrication conditions in presence of oil containing MoDTC

Abstract Tribological behaviour of steel APS coating and TiO 2 APS coating was investigated and compared with reference steel material under boundary lubrication in presence of MoDTC. Significant friction and wear reduction was observed in case of TiO 2 APS coating compared to conventional steel and steel APS coating. This was due to the formation of pure MoS 2 in the form of long crystalline flakes directly attached to TiO 2 substrate. Friction was slightly higher in case of steel since Mo-oxysulphide formation was observed along with some MoS 2 flakes embedded in an amorphous matrix. Effect of roughness and addition of ZDDP on MoDTC decomposition mechanism was discussed. Tribocatalytic effect was proposed to explain the complete decomposition of MoDTC in steel/TiO 2 APS contact.