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In this work, the lubricating models of Cu–Zn alloy with and without the Zinc oxide (ZnO) layer were established. Molecular dynamics (MD) simulation is employed to investigate the lubrication behavior of n-hexadecane on the ZnO layer at the nanoscale. The diffusion of lubricants molecules, and the interaction and stick–slip effect between the friction pairs and the lubricants are systematically explored. The results show that the ZnO layer limits the diffusion of n-hexadecane molecules and the formed lubricating films in the model of the substrate with the ZnO layer are obvious and stable. During the sliding process, ZnO molecules have strong interaction with lubricants molecules and adsorb lubricants molecules on the surface to form adsorption film. The stick–slip effect in the lubricating films generates periodic shear stress and reduces the wear of the friction pair. The ZnO layer causes lubricants molecules to be arranged regularly on the surface into a stable structure. [ABSTRACT FROM AUTHOR]

The nanoscale friction behavior of quartz-quartz and quartz-kaolinite interfaces is investigated through Steered Molecular Dynamics (SMD) simulations. The effects of normal load, sliding velocity, temperature, and hydration on the friction behavior are discussed, and the friction mechanism of quartz and quartz/kaolinite interface is revealed. The friction coefficients of all systems at different cases are obtained and compared with other experimental results for validation. The simulation results show that the stick-slip effect in all interfaces was found during the friction process, where the higher the sliding velocity and hydration, or the lower the normal load, the weaker the stick-slip effect. The friction load increased with the rising normal load, and the relationship between shear stress and normal load was approximately linear. The friction coefficient and cohesion of the quartz-quartz interface could rise with the increasing sliding velocity or the decreasing temperature. Moreover, the friction coefficient of quartz-kaolinite was significantly smaller than that of quartz-quartz, indicating that the presence of clay could weaken the frictional strength of quartz. The effect of the interlayer water film on friction behavior was rather complex, showing the lubricating or bonding role, which has been discussed and analyzed in the present study. [Display omitted] • The stick-slip effect was found in the quartz-quartz interface during the friction process. • The higher the sliding velocity and hydration, or the lower the normal load, the weaker the stick-slip effect. • The presence of clay could weaken the frictional strength of quartz. • Friction coefficient and cohesion of quartz rose with the rising sliding velocity or decreasing temperature. • The relationship between shear stress and normal load was linear in nanoscale friction. [ABSTRACT FROM AUTHOR]