In-situ formed carbon based composite tribo-film with ultra-high load bearing capacity

Abstract Forming carbon based tribo-film in situ is an environmentally friendly and efficient way to solve the boundary lubrication problem. In this paper, the cubic nickel nanoparticles (average particle size 21.3 nm) modified by oleylamine were used as additives of poly-alpha-olefin (PAO6) for extreme pressure (EP) lubrication between bearing steel and stainless steel. It was found that in the range of 1.4–2.2 GPa contact pressure, nickel nanoparticles can catalyze the carbonization of PAO6 on the friction surface, which reduced the wear rate by 94%, the friction coefficient (COF) by 79%, and can withstand the extreme pressure friction of 4.2 GPa. XPS, EDS, TEM and FIB were used to analyze the microstructure, composition and chemical state of tribo-film. The tribo-film is composed of oxide layer, concrete structure layer and amorphous carbon layer. The oxide layer formed by oxidation of steel surface produced better binding force with the steel substrate. Nickel nanoparticles catalyze the carbonization of PAO6 to form a concrete structure with nickel nanocrystals embedded in the amorphous carbon phase, which provides high bearing capacity. The carbon layer graphitizes under the friction induction to form a lubricating layer with low friction characteristics. Oleylamine modified nickel nanoparticles is expected to be widely used as an environmentally friendly EP additive.