Friction and wear performance of copper-graphite surface composites fabricated by friction stir processing (FSP)

Copper-graphite composites which have low friction coefficient can be used as bearing materials in lieu of materials containing lead which cause environmental problems. So far, some methods such as powder metallurgy and centrifugal casting have been employed to produce these composites. In this study, friction stir processing (FSP) was used to produce copper-graphite surface composites. Five tools with different pin profile were employed in order to achieve a comprehensive dispersion. Results show that the tool with triangular pin gives rise to a better dispersion of graphite particles. Furthermore, four copper-graphite composites containing different graphite content were prepared using triangular tool through repeating the process passes. Friction and wear performance of the composites were studied using a pin-on-disc tribometer. It was indicated that the friction coefficients of composites were lower than pure annealed copper and decreased with increase in graphite content. The reduction in friction coefficient is due to decrease in metal-metal contact points, originated from the presence of graphite particles as a solid lubricant. Wear loss of the composites was also decreased with increase in graphite content. This is related to change in wear mechanism from adhesive to delamination wear and reduction of friction coefficient.