Tribological studies on microwave sintered copper–carbon nanotube composites

Multiwall carbon nanotubes were coated with copper using an electroless two-step sensitization–activation method in order to improve the interfacial strength of the metal matrix. Copper-coated carbon nanotubes (5–20 vol.%) were mixed with copper metal powder and microwave heating was used to sinter them. The composites were subjected to pin-on-disc testing to study their tribological characteristics. Their mechanical and tribological properties were comparable to those of conventional and spark plasma sintered ones. The improvement in properties was limited to 15 vol.% due to the agglomeration of carbon nanotubes. The composites exhibited a lower coefficient of friction and a lower wear rate compared to unreinforced copper, because of the formation of a carbonaceous film at the contact surface. The self lubricating effect of carbon nanotubes reduces the frictional heating. The wear mechanism for low carbon nanotube concentrations was plastic deformation, whereas at high concentrations it was flake formation/spalling.