Synthesis & Characterization of Copper-Graphite Metal Matrix Composite by Powder Metallurgy Route

Abstract

Copper–graphite metal matrix composites possess the properties of copper, i.e. excellent thermal and electrical conductivities, and properties of graphite, i.e. solid lubricating and small thermal expansion coefficient. They are widely used as brushes, and bearing materials because of the above properties. Copper-graphite with low percentages of graphite is also used for slip rings, switches, relays, connectors, plugs and low voltage DC machines with very high current densities. In the present investigation, attempts have been made for the fabrication of Cu-graphite MMC by conventional and spark plasma sintering (SPS) techniques. The MMCs were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Different mechanical properties like density, bulk hardness and wear study were also conducted. XRD spectra show the presence of Cu, graphite and Cu2O peaks which shows that no interaction between Cu and graphite takes place during fabrication. The presence of a weak peak of Cu2O proves that slight oxidation of Cu takes place during sintering. It has been found that addition of graphite into copper does not result in much improvement in hardness due to the soft nature of graphite. However, 90% and 97 % of theoretical density have been obtained for conventional sintered and SPS samples respectively. Maximum Vickers hardness value of around 100 has been achieved for Cu-1 vol. % graphite MMC when it is fabricated by SPS. However, a hardness value of 65 has been obtained for the same composite when it is fabricated by conventional sintering at 900°C for 1 hour. The micrographs of Cu-graphite reflect the clean interface and good compatibility between matrix and reinforcement. From wear study, it is concluded that the wear resistance of the composite increases with increase in graphite content due to the lubricating properties of graphite. It has also been found that wear depth decreases with increase in graphite content. SPS sintered samples show higher wear resistance than conventional sintered samples.