Microstructural Characterization of Copper-Carbon Composites

摘要

Copper-carbon composites, nominally containing up to 50 volume percent additions of graphite, were produced from thoroughly ball-milled powder mixtures by sintering under vacuum at different temperatures in the range from 400 to 800℃. The microstructure of as-milled powders and sintered products have been mainly characterized by scanning and transmission electron microscopies, x-ray diffraction and energy-dispersive x-ray spectrometry. SEM and TEM characterization of the as-milled powders showed that the mixing of the original copper and graphite powders reached submicrometer level, with a tendency for the graphite to completely coat the copper particles. XRD and TEM characterization also indicated the presence of substantial amounts of copper oxides in the mechanically alloyed powders. After sintering, the dispersion of graphite in the copper matrix remained at the submicrometer scale for sintering temperatures up to 600℃. However, specimens sintered at 800℃ showed a clear separation process of the copper and carbon constituents. The amount of oxides found in the powder mixtures decreased as the sintering temperature increased, particularly in the Cu-50 vol% materials, but this occurred at the expense of gas evolution as a result of the reduction of the oxides by the carbonaceous component and, in some cases, unacceptable porosity levels. It is shown that composite copper-graphite composite powders produced by means of the mechanical alloying process have the potential of providing considerable flexibility in the control of microstructural features in the bulk composite materials derived therefrom.