Lubrication Mechanisms of Core–Shell Ag@Cu Microparticles as Lubricant Additives in EHC-50 Base Oil

Abstract

Lubricant additives play a crucial role in improving the tribological performance of lubricating oils to reduce frictional energy losses and improve the durability and reliability of mechanical systems. In this study, soft metallic-based core–shell Ag@Cu microparticles were synthesized via an in-situ galvanic displacement method and incorporated into EHC-50 base oil with various concentrations. The tribological performance evaluations indicated that 0.3 wt% Ag@Cu significantly enhanced friction-reducing and anti-wear properties, achieving a stable friction coefficient of 0.12, a 45% reduction, and a wear volume reduction of 75% compared to the pristine oil. Additionally, the surface characterization techniques (SEM/EDS, XPS, XRD, and TOF-SIMS) were employed to explore the wear patterns and related lubrication mechanisms. The results indicated that the synergistic interaction between the micro-bearing effect, physical mending, and tribochemical reactions facilitated the formation of a robust tribofilm composed of metallic Ag, ternary CuFe3O2, and sulfides, which achieved higher lubrication performance. Ultimately, this research provides novel metallic micro-additives, offering a facile approach to formulating wear-resistant lubricants with significant potential for saving energy for mechanical tribosystems in industrial applications.