Robust macroscale superlubricity on carbon-coated metallic surfaces

This paper discusses experimental and computational results of ultralow (near-zero) friction of carbon-coated metallic depositions on substrates of structural steels, Ti, and Ni alloys. The macroscale superlubricity was demonstrated and sustained over several cycles through structurally misoriented carbon coatings on the metallic surfaces. Carbon nanocrystals with variants of graphene footprints were deposited on these metallic surfaces using a novel high temperature biowaste treatment process. The carbon nanocrystals deform, flatten, and coalesce in the wear tracks to form graphitic films leading to a superlubricious coefficient of friction of ∼0.003. A coating life of ∼150,000 cycles with reduced wear rates was obtained on Ni and steel substrates. The experiments were validated with atomistic simulations providing mechanistic insights into the effects of the graphene variants on the observed frictionless conditions. The underlying mechanisms of the coating/substrate interactions contributing to the macroscale superlubricity are elucidated. The implications of the current results are explored for designing robust and low-cost macroscale superlubricious carbon coatings on metallic substrates. Biowaste is a carbon source within a circular economy that uses material recycling to reduce the global carbon footprint.