Tribological and mechanical characterization of epoxy/graphite composite coatings: Effects of particles' size and oxidation

The present study investigates the mechanical and tribological properties of an epoxy matrix filled with different graphitic particles deposited on an aluminum substrate by the electrostatic spray technique. Three different particles added to the epoxy matrix were the received graphite, the crushed graphite obtained by crushing the natural flake graphite particles using a ball mill, and graphite oxide obtained by oxidation treatment. Nanoindentation tests were conducted on the different coatings in order to evaluate the surface hardness and the contact elastic modulus. The effect of the oxidation treatment and the loading content on the tribological behavior of the above composites were also evaluated under dry-friction conditions. As expected, the smaller the particle size, the greater the reduction in the dynamic friction. The experimental findings showed that adding 5 wt % of crushed graphite (10 mu m) provided a similar dynamic friction as the addition of 10 wt % of received graphite (20 mu m). The epoxy filled with received graphite showed a lower wear rate than that filled with graphite oxide and crushed graphite. Moreover, both hardness and elastic modulus increased in the case of the epoxy filled with graphite oxide and crushed graphite.