Carbon-based films: A review on mechanical and tribology properties

Abstract

Carbon films have attracted widespread interest for decades thanks to their superior tribomechanical properties. As new carbon allotropes were discovered over time, measurements of elastic modulus reached terapascals, and coefficient of friction thousandths, while the mechanisms that enabled this performance were understood. Yet, research attention on carbon-based films and composites is still increasing by the year. Challenges such as durability and chemical reactivity have been addressed by doping and surface passivation, and the combination of two or more carbon allotropes in a single film, as in merging carbon nanotubes and nanodiamond in forming nanoscrolls, allowed to combine the superior properties of each, achieving a performance which is higher than either material alone. This review is focused on films based on various forms of carbon, including amorphous carbon, diamond-like carbon, graphite, graphene, carbon nanotubes, nanodiamond, fullerenes, and their hybrids. The tribomechanical properties, as well as the underpinning mechanisms than enable them, are explored. The effect of chemical composition, environment, structure, scale and substrate are presented, in relation to performance. Finally, some examples of composite materials whose performance is enabled by the addition of carbon-based materials are presented. Ways forward in the field are identified, in particular within the hybrid and composite materials areas, which have the potential of further increasing applicability and performance of carbon-based films.