Turbulence-like Cu/MoS2 films: Structure, mechanical and tribological properties

Abstract

The application of pure molybdenum disulfide (MoS 2 ) film as solid lubricant is limited due to its low hardness and high friction coefficient in the atmosphere. It is reported that the hardness can be improved by doping metal elements into MoS 2 , while the friction coefficient can be reduced by the formation of curved micro-nano structure of MoS 2 . Thus, doping metal atoms with catalytic properties such as Cu into MoS 2 , to form turbulence-like micro-nano structure has the potential to simultaneously increase hardness and decrease friction coefficient. In our work, we deposit Cu/MoS 2 films with turbulence-like structure (TL-MoS 2 ) using magnetron sputtering technology, which exhibit higher hardness and lower friction coefficient in the atmosphere than pure MoS 2 . When the Cu content reaches 15.9 at.%, Cu atoms with catalytic properties induce the formation of curved S-Mo-S layers and forms TL-MoS 2 . Cu incorporation results in the change of preferred orientation of film from (100) plane for pure MoS 2 to (002) plane for Cu/MoS 2 , accompanied by the densification of the structure. The hardness of Cu/MoS 2 is approximately 10 times higher than that of pure MoS 2 due to the denser structure and TL-MoS 2 . It is worth mentioning that TL-MoS 2 contributes to the improvement of the hardness by extending the strength of the planar network into a three-dimension space network. Moreover, TL-MoS 2 prevents oxidation and promotes the formation of MoS 2 tribofilm during sliding, leading to a significant reduction of the friction coefficient to 0.07 ± 0.01 in the atmosphere, which is 3 times lower than that of pure MoS 2 film. Our strategy provides guidance for preparing metal doped MoS 2 films with excellent mechanical and tribological properties for application in the atmosphere. • Doping Cu into MoS 2 induces the formation of turbulence-like MoS 2 . • The hardness of Cu/MoS 2 film is 10 times higher than that of pure MoS 2 film. • The COF of Cu/MoS 2 film in the atmosphere is much lower than that of pure MoS 2 film. • The Cu/MoS 2 film has the potential as lubricious and protective coating in the atmosphere.