Frictional properties of diamond and fullerene nanoparticles sprayed by a high-velocity argon gas on stainless steel substrate

Lubricating abilities of diamond nanoparticles with size between 50 nm and 200 nm were studied in vacuum and in air to clarify the effective use of diamond fine powders for tribological purposes. Spraying of powders with a high-velocity argon gas jet was performed to form deposits on stainless steel (SUS304) substrates. For sliding in vacuum against SiC and Al2O3 balls under a 0.5 N applied load and 3.5 mm/s sliding speed, the deposits of microcrystalline diamond powders with a mean particle size of 50 nm and detonation nanodiamond with a mean aggregate size of around 75 nm demonstrated friction coefficients of less than 0.01 and 0.03, respectively, and ball wear rates of less than 2 · 10− 6 mm3/(Nm). This means that diamond fine powders smaller than 100 nm can be considered as good solid lubricants in vacuum, because they demonstrate not only a low friction coefficient, but also wear rate of SiC ball lower than non-lubricated SUS304 does. A C60 deposit, formed by the same method on the SUS304, was readily scratched from the substrate in vacuum; however, under open-air conditions, a friction coefficient of around 0.1 and a SiC ball wear rate of about 2 · 10− 6 mm3/(Nm) were observed. This fact calls attention to the influence of the deposition method on C60 frictional properties.