Influence of surface roughness and running-in on the lubrication of steel surfaces with oil containing MoS2 nanotubes in all lubrication regimes

► Lubrication of steel with MoS2 nanotubes in PAO oil in all lubrication regimes. ► The MoS2 nanotubes reduced friction by 40-65% compared to pure PAO oil. ► Nanotubes governed the friction behaviour, rather than roughness and running-in. ► Surface roughness did not affect the friction behaviour of the MoS2 nanotubes. ► Running-in did not change the performance of the MoS2 nanotubes in the contacts.