Superlubricity of MoSxOy/H-DLC composite in dry and moist air

The engineering application of superlubricity in dry and moist atmospheres is critical for reducing friction, wear, and economic consumption. The MoS₂/H-DLC composite can achieve superlubricity in oxygen, which can help to quickly form a MoS₂ transfer film on the surface of counterpart at the initial sliding stage. However, the friction performances of MoS₂/H-DLC composite were still unclear in dry and moist air when these MoS₂ flakes were doped with oxygen. Regarding this problem, we constructed some MoS_xO_y/H-DLC composites with different degree of oxidation, and their friction performances were investigated in dry and moist air with relative humidities of approximately 10 %, 20 %, and 30 %. Superlubricity was achieved by the composite in dry and moist air with a relative humidity of approximately 10 %. Raman, AFM, SEM-EDS, and TEM characterizations have been conducted to reveal the composition and structures of these as-formed wear scars and tracks. These results suggested that a small number of water molecules in the atmosphere could promote the formation of the MoS_xO_y transfer film on an Al₂O₃ ball, which was crucial for achieving superlow friction in moist air. These findings provide some helpful suggestions for obtaining superlow friction in moist air.