The Effect of Graphite on the Processing and Properties of Copper-Graphite Composites

摘要

Copper-graphite composites containing up to 30 vol.% of graphite were prepared by powder processing. Three types of graphite, i.e., flake type pure graphite, copper-coated graphite and short fiber, were utilized for the composites. The addition of more than 10 vol.% pure graphite was not possible due to compaction cracking, whereas the coated graphite or fiber up to 30 vol.% caused little problem when compacted to 80-85% theoretical density (TD). The use of coated powder also improved sintering, increasing the sintered density close to 90% TD as compared to more than 5% decrease of density when only 5 vol.% of the pure graphite was added. Transverse rupture strength of the sintered specimens decreased steadily with increasing the graphite content from over 30kN/cm~2 for pure copper to 10kN/cm~2 with 20 vol.% graphite. Fully densified composites were produced by hot pressing or hot extrusion. The latter process caused strong graphite alignment to the extrusion direction and the resulting properties also showed some anisotropy. Thermal conductivity of about 300W/mK and thermal expansion coefficient of 11 ppm were obtained with the fully densified composite of 20 vol.% graphite on a longitudinal direction.