Insights into robust carbon nanotubes in tribology: From nano to macro

Over the years, reducing friction and wear-induced deformation, damage and/or removal of material at various contact interfaces has always aroused significant interests due to the substantial benefits for impaired machinery components, as well as the efficiencies in energy and economy. Among numerous advanced nanomaterials, carbon nanotubes (CNTs) have been recognized as solid lubricants, or additives in the liquid/solid material systems (coatings, composites and lubricants) to effectively reduce friction and wear. This is well-motivated by CNTs' hollow tubular nanostructure and outstanding physicochemical properties which can potentially support them with many favorable frictional mechanisms, such as filling/mending effect, sliding/rolling effect, and tribofilm-forming effect. Despite the enormous efforts pertaining to CNTs for tribological optimizations, discussing them across the nano-scale to macro-scale for the understanding of critical interactions between the CNTs and contact objects remains rarely explored. In this review, the state-of-the-art advances in computational tribology research of the CNTs and their significant nano/macro-tribology mechanisms in related systems are methodically provided, beginning with a brief overview of CNTs on their manufacturing, structural properties, and functionalization. Additionally, we present a condensed summary of the encouraging findings, accompanied by some valuable recommendations for the sustaining prosperity of CNTs in tribology.