The effect of milling and sintering techniques on mechanical properties of Cu–graphite metal matrix composite prepared by powder metallurgy route

Abstract

When copper is used as electrical sliding contacts, a large contact force is desirable to maintain effective current transfer, whilst on other hand it is advisable to have as small as contact force as possible in order to reduce the wear of the sliding components. In the present investigation Cu–graphite metal matrix composites (MMCs) were prepared by conventional powder metallurgy route using conventional and spark plasma sintering (SPS) techniques. It has been found that addition of graphite into copper does not result in much improvement on the hardness due to the soft nature of graphite. However, 90% and 97% of relative density have been obtained for conventional sintered and SPS samples respectively. Maximum Vickers hardness of around 100 has been achieved for Cu–1vol.% graphite MMC when it is fabricated by SPS due to the combined effect of pressure and spark plasma effect. However, a hardness value of 65 has been obtained for the same composite when it is fabricated by conventional sintering at 900°C for 1h. It has been found that density and hardness of MMCs decreases up to 20h of milling due to flake formation and increase in size and after that these values increases as particle shape changes to irregular and size reduction takes place.