Nanocrystalline Graphite Formed at Fullerene-Like Carbon Film Frictional Interface

High performance solid lubricant materials with long wear life remain as one of the challenges in space technology. It is of great significance to lower the solid film's friction and wear and to prolong its service life in vacuum. Hydrogenated fullerene-like carbon film produced by dc-pulsed power source behaves ultralong wear life (>> 1.8 x 10(5) cycles) and ultralow wear rate (2.2 x 10(-8) mm(3) Nm(-1)) as well as low friction (approximate to 0.14) in high vacuum (2.3 x 10(-4) Pa). To understand its long wear life reason, the interfacial structural evolution is investigated after steady state friction is achieved. By observing the interfacial nanostructure evolution, it is found that the friction and wear properties are related to the friction-induced phase transformation from fullerene like structure to nanocrystalline graphite and the deposition of tribofilm on Al2O3 counterface. And this process is analyzed by X-ray photoelectron spectroscopy, micro-Raman spectra and is observed through transmission electron microscopy. The results enrich hydrogenated fullerene-like carbon film friction mechanisms and expand its potential application in space.