Vacuum Tribological Performance of WS2–MoS2 Composite Film Against Oil-Impregnated Porous Polyimide: Influence of Oil Viscosity

To achieve the desired levels of performance and durability for bearings applied in space, a novel solid–liquid dual lubricating system was established via the WS2–MoS2 composite films sliding against oil-impregnated porous polyimide (PPI), in which polyalphaolefin (PAO) oils with different viscosities were used, respectively. The contact angle measurement indicated that the PAO oil had good wettability on the surfaces of the composite film and the PPI. The vacuum tribological behaviors of single WS2–MoS2 composite film and the dual lubricating system were mainly evaluated under different loads and speeds. In comparison with single WS2–MoS2 composite film, the dual lubricating system exhibited the low friction coefficient and synergistic lubricating effect for the low-viscosity PAO oil under severe sliding conditions. It was concluded that the cleavages of the WS2 and MoS2 crystals along the basal plane were more sufficient and formed small and thin WS2 and MoS2 platelets in the dual lubricating system. Meanwhile, it was found that oil-impregnated PPI readily released PAO lubricating oil with low viscosity, which further decreased friction on the contact interface. The lubricating mechanism of the dual lubricating system was also revealed after correlating the tribological behaviors of the different lubricating systems.