Interfacial interaction induced synergistic lubricating performance of MoS2 and SiO2 composite nanofluid

SiO2 was employed as an auxiliary lubricant for MoS2 nanofluid to gain superior lubricating effect. Tribological properties and cold rolling lubrication performance of pure SiO2 nanofluid, pure MoS2 nanofluid and the MoS2+SiO2 composite nanofluid were investigated to reveal the synergistic lubrication of MoS2 nanosheets and SiO2 nanoparticles. The results of tribological tests indicated that the composite nanofluid with kappa (mass ratio of MoS2 and SiO2) >= 1 showed more excellent tribological properties than pure MoS2 nanofluid depended on a low shear composite lubricating film formed on steel surface. The formation mechanism of the composite lubricating film was investigated through both experimental characterization and molecular dynamics simulation. During cold rolling process, SiO2 nanoparticles which did not readily adsorb to steel surface firstly absorbed on the surface of MoS2. And then adsorb on the steel surface together with MoS2 in virtue of the adsorption between MoS2 and steel surface. A pressurized interlayer slip theory was creatively provided to explain the synergistic lubrication mechanism of the low shear composite lubricating film. The SiO2 adsorbed on MoS2 nanosheets changed the contact type between MoS2 nanosheets from surface contact to point contact. Thus, the normal pressure on the surface of MoS2 nanosheets was increased. According to the results of molecular dynamics simulation, the increase of normal pressure promoted the interlayer slip and reduced the friction coefficient between MoS2 nanosheets. The relationship between lubrication mechanism and the mass ratio of MoS2 and SiO2 was also investigated to provide a systemic understanding of the synergistic lubrication performance.