Tribological Properties of SiO2@Cu and SiO2@MoS2 Core–Shell Microspheres as Lubricant Additives

Herein, core–shell structural SiO2@Cu and SiO2@MoS2 microspheres were prepared using SiO2 as hard core, Cu and MoS2 as shell. As lubricant additives were introduced into base oil (PAO 40), their friction reduction and wear resistance were investigated in detail. Comparing with onefold additive (SiO2, Cu and MoS2), such core–shell structural additives can improve the tribological behaviors at the Hertz contact stress range of 1.26–2.72 GPa (SiO2@Cu reduces the friction and wear up to 32.47% and 67.86% at 2.72 GPa, respectively). Besides, the tribological properties of SiO2@Cu microspheres are superior to that of SiO2@MoS2 (the wear volume was reduced by 48.45% at 2.72 GPa). The excellent tribological behaviors of SiO2@Cu microspheres can be ascribed to its structural advantage, the synergistic effect of hard SiO2 core and Cu shell. The rolling effect of SiO2, easy-shearing and self-repairing of Cu shell offer a synergistic lubrication function and form a dense protection film, thereby contributing to the optimal lubrication performance.