A comprehensive review of electro-tribological behavior in conductive lubricants

The electric machinery industry is currently facing a significant challenge in the application of electrical contact materials with appropriate electrical and tribological performance. The use of conductive lubricants, including liquid, solid, and semi-solid varieties, represents a key approach to meeting technical and sustainable criteria. This strategy is closely linked to the development of multifunctional additives with excellent conduction properties in response to the growing concerns regarding the increased durability of electrical equipment. This paper provides a comprehensive review of prior research in this area, specifically studies investigating conductive lubricants incorporating conductive additives and demonstrating exceptional electro-tribological properties. Various conductive additives have been incorporated into these lubricants, each providing unique advantages, such as enhancing conductive connectivity, reducing friction and wear, and improving the dispersion of other functional additives. This review covers a range of conductive materials, including carbon-based materials (carbon nanotubes, graphene nanosheets, carbon black, etc.), ionic liquids, metals (soft metal-based composites, gallium-based liquid metals), MAX phases, semiconductors, and conductive polymers, and discusses their impact on the electrical conductivity and electro-tribological properties of conductive lubricants. Additionally, the electro-tribological properties of insulating lubricants are introduced. Promising conductive lubricants are identified based on comparisons of their electrical conductivity, coefficient of friction (COF), wear rate, and electrical contact resistance (ECR) under various current-carrying friction (CCF) conditions. In conclusion, it is found that conductive lubricants effectively reduce friction and wear under current-carrying conditions, thus contributing to the advancement of the electrical machinery industry. This paper also outlines potential research directions in this field, pointing to the promising future of conductive lubricants in enhancing the performance and sustainability of electrical equipment.