Microstructure and lubrication mechanism of multilayered MoS2/Sb2O3 thin films

Multilayered MoS2/Sb2O3 thin films were prepared by pulsed laser deposition on steel substrates. A rotary multi-target holder was used to switch the laser targets for alternative growth of MoS2 and Sb2O3 layers providing nanometers thickness. The tribological properties of the films were measured in dry and wet environments and the wear scars were observed using a scanning electron microscope. The multilayer films showed a much longer wear life than pure MoS2 films in wet air tribotests. Focused ion beam and transmission electron microscopies were used to investigate the cross-sectional microstructures of wear scars. Lubricious MoS2/Sb2O3 tribofilms were built up on wear scar surfaces, and produced low friction. Micro-cracks occurred along the interface between the tribofilm and the neighboring/topmost Sb2O3 underlayer, where the Sb2O3 layer effectively inhibited the crack propagation perpendicular to the interface. The orientation of MoS2 crystals in as-deposited films was mostly random and friction-induced stress oriented the MoS2 basal planes parallel to the surface. The reorientation was confined to the topmost MoS2 layer and was not observed below the first intact Sb2O3 layer.