Enhancing mechanism of nanodiamonds on tribological behavior and antiwear properties in Ag composite coatings during current-carrying friction

Introduction of hard phases into soft metal coatings is a widely used strategy to improve the tribological behavior and antiwear properties during current-carrying friction. In this work, we developed silver (Ag) composite coatings reinforced with nanodiamonds (NDs) using a self-devoloped rotating spray deposition technology. The composite coatings, with a 0–10 g/L rage concentrations of NDs, were comprehensively characterized for morphology, chemical composition, hardness, and current-carrying tribological behavior and antiwear properties. Thanks to the unique advantages of our fabrication technique, the coatings show a dense structure with strong interfacial bonding both at the coating-copper substrate interface and between the Ag matrix and NDs in composite coatings. The addition of NDs not only maintains excellent electrical conductivity (minimum 98.1 %ICAS) but also boosts microhardness to 169 HV. Uniformly dispersed NDs effectively enhance the tribological behavior and wear resistance, keeping the friction coefficient stable at 0.1–0.2 and reducing the wear rate significantly with the shallowest wear track measuring only 6 μm. Finally, the worn subsurface structure of wear tracks was analysized to confirm the good bonding between NDs and the Ag matrix, as well as the dispersion-strengthening effect of NDs within the Ag matrix and the plastic deformation mechanism of Ag during current-carrying friction. This study not only enriches the enhancing mechanism in hard-phase-reinforced composites but also provides new insights and approaches for the development of electric contact coating materials.