Effect of Reinforcement of Carbon Nanotube, Graphite or Carbon Fibre with Different Addition Amounts on Tribological Properties of Polyimide Coating

Carbon nanotubes, graphite, and carbon fibers reinforced polyimide （PI） composite coatings on friction block surfaces were prepared separately by a stepwise temperature curing process. The addition amount （mass fraction） of fillers was 0.2%, 0.4%, 0.6%, 0.8%, 1.0%. The effect of the reinforcement of different fillers on the imidisation degree of PI, and tribological properties of the coatings were comparatively investigated. The results show that all three fillers improved the imidisation degree of PI. The PI composite coatings reinforced by carbon nanotubes had the highest imidisation degree and the greatest magnitude of increase in the hardness of transfer film. With the increase of addition amount of fillers, the friction factor and wear rate of the composite coatings were basically decreased first and then increased, and the friction factor and wear rate were the smallest when the filler mass fraction was 0.6% under most conditions. The quality of transfer film on surface formed during friction of PI coatings was improved by the addition of filler with 0.6% mass fraction, and the hardness of the transfer film was increased. The best transfer film quality and the greatest hardness increase were achieved by the addition of carbon nanotube.