Influence of preload on the tribological performance of MoS₂/GO composite lubricating coating

Lubrication is one of the key factors to ensure the reliable operation of sliding parts for some critical components in aerospace. The most favorable lubrication performance of the lubricating film is always achieved after the initial period or the pre-running-in period. In this work, the influence of preloads varying from 0.5 to 15 N on the tribological performance of molybdenum disulfide/graphene oxide (MoS₂/GO) composite lubricating coating was studied. It was found that the coefficient of friction (COF) during the running-in period decreased from 0.17 at 0.5 N to 0.14 at 5 N, and stabilized at 0.14 with further increasing the normal load, indicated that the optimal stable COF was obtained at 5 N and negligible changes when load is further increased from 5 to 15 N. In contrary to the widely reported coatings that their tribological results deteriorate at high applied loads, the MoS₂/GO composite lubricating coating here exhibits much lower COF under higher loads, with the COF decreased from 0.14 at 5 N to 0.03 at 100 N. The results suggests that the preload had a positive effect on the tribological performance of the MoS₂/GO composite coating, the COF of the composite coating decreased with the increase of the preload, which further improved the tribological properties and even achieved the optimized lubrication condition, and the optimum preload was equal to or slightly higher than the steady-state load. This work provides a guiding idea for the selection strategy of the preload for optimal tribological performance of the solid lubricating coating.