Macroscale Superlubricity Enabled by Graphene Nanocomposite Films on Metallic Surfaces

Globally, ~100 million terajoule of energy is required to reduce friction, accounting to a fifth of energy generated annually. About 1 – 4% of the Gross Domestic Product (GDP) of industrialized economies is spent on friction and wear phenomena. Ultra-low friction at micron and nano scales have been achieved by application of graphene and its variants, due to their excellent lubrication properties. However, depositing these carbon-based coatings on substrates at the macroscale is challenging and expensive. The mechanisms of superlubricity is also not fully understood. In this work, graphene-like coatings with multiwalled graphene signatures were deposited on Ni, Ti, Ti-6Al-4V and AISI 1045 steel. The method used for the deposition process was a novel low-cost high temperature biowaste treatment at 900^oC. Wear behaviour using ball-on-disk configuration on the bulk coated metallic substrates were investigated. Microstructural features and Raman scattering of the as received and worn surfaces were characterized. The results showed sustained ultra-low friction and wear on the bulk metallic surfaces with the lowest coefficient of friction value of 0.003. This was attributed to the coated carbon nano crystals deforming to graphene nano composite films, providing the needed incommensurability and multiple micropoints interactions for frictionless conditions. The wear rates of the treated substrates were drastically reduced. The underlying tribo-oxidation and stress induced tribo-transformation controlled interactions and mechanisms were elucidated, before exploring the implications of the current results for the design of robust and next generation 2D and 3D carbon-based coatings with frictionless property at the macroscale.