Tribological Behavior of Copper–Graphite Powder Third Body on Copper-Based Friction Materials

Tribological behavior of copper–graphite powder third body on copper-based friction materials was investigated by adding different percentage copper–graphite mixed powder into the friction surface during dry sliding. Friction tests were conducted under different friction speeds (100–1500 rpm) at the pressure of 0.51 MPa by a pin-on-disk tribometer. The morphology of copper–graphite third body was observed, and the formation mechanism was explained. The results indicate that the friction coefficient is decreased by the presence of exogenous copper–graphite powder on the friction surface. The average friction coefficient is 0.03, 0.12, 0.21 and 0.22 lower for exogenous copper 90 wt%–graphite 10 wt%, copper 50 wt%–graphite 50 wt%, copper 10 wt%–graphite 90 wt% and exogenous pure graphite powder than the non-exogenous case, respectively. The decrease in the friction coefficient is attributed to the good flow ability and lubricity of graphite particles on the surface, which reduces the adhesion between the metal materials. At low speed, the adhesive graphite stacking as solid lubricant particles decreases the amount of copper combination and alleviates the plastic deformation of copper, which leads to a low and stable friction coefficient. At high speed, owing to delamination wear, graphite smears upper the surface, prevents a metal-to-metal contact and acts as a lubricant layer between the tribocouple; thereby, the friction coefficient decreases.