Superior tolerance of nanocrystalline diamond films to Heavy-ion Irradiation: Maintenance of solid lubrication properties

Abstract By varying the CH4 content of the mixed gas precursor of hot-filament chemical vapor deposition, a group of nanocrystalline diamond (NCD) films was fabricated in a dual nanostructure with well-controlled growth of small and large grains with sizes of 5–10 and ∼ 200 nm, respectively. The irradiation resistance and tribological properties of the NCD films were studied before and after irradiation (by 3.25-MeV Xe15+ ions), and various characterization techniques were adopted to investigate the evolution of the bonding structures and tribological properties of the studied films. All the radiated films exhibited the same amorphous structure in the depth of the projected range and showed comparable lubricant properties and wear rates (1.2 × 10-7–1.9 × 10-7 mm3/N‧m), regardless of how the grain sizes changed in the range of 5–200 nm. Moreover, the friction coefficients of the radiated films were relatively lower and more stable than those of the pristine films, because of the radiation-induced reduction in the surface roughness and the formation of tribofilms with a graphite-like structure. The excellent maintenance of lubrication properties after heavy-ion irradiation provides a feasible route for the development of anti-irradiation films for use as a solid lubrication material in nuclear irradiation environments.