Humidity‐Resistant Ultralow Friction in Diamond‐Like Carbon Coatings Enabled by Graphitic Nanodiamonds

Hydrogenated diamond-like carbon (H-DLC) coatings are extensively employed in high-performance tribological applications, yet their frictional behavior in humid environments remains a critical limitation. A scalable and industrially viable strategy based on graphitic nanodiamonds (Gr-NDs) is here proposed, enabling humidity-resistant ultralow friction (coefficient of friction  <0.1) without requiring controlled atmospheres or complex surface treatments. This approach is distinct from many recent methods involving the deposition of nanoparticles and 2D materials, which often fail under humid conditions. Gr-NDs leverage their intrinsic core–shell nanostructure to promote the in operando formation of a peculiar graphitic transfer layer (TL), directly enhancing interfacial lubrication. High-resolution transmission electron microscopy and Raman spectroscopy confirm that these nanostructures are effectively retained within the TL, ensuring superior wear resistance and friction reduction. Furthermore, spectroscopic analysis reveals that moderate tribochemical oxidation stabilizes the TL, extending its durability under realistic operating conditions. This work establishes Gr-NDs as a disruptive functional additive for H-DLC coatings, offering a robust, scalable, and environmentally friendly solution for next-generation tribological systems in demanding mechanical applications.