Hybrid effect of graphite and carbon fibers on thermal properties of copper/ graphite/carbon fibers composites

To maintain the high thermal conductivity (TC) and reduce the coefficient of thermal expansion (CTE) of conventional copper (Cu)/graphite composites, novel Cu/graphite/carbon fibers (CFs) hybrid composites were designed by replacing part of graphite with Cu-coated CFs and prepared by spark plasma sintering (SPS) process. The incorporation of CFs resulted in increased interface density, reduced twin boundaries, and significant grain refinement of the Cu matrix. TEM observations revealed that the Cu-coating on surfaces of CFs enhanced the interfacial bonding between CFs and Cu matrix. The Cu-coated CFs can act as connecting channels between graphite particles, which partially compensate the negative effect on TC. Furthermore, strong interfacial bonding and large Cu/CFs contact areas contribute to the reduction in CTE. As a result, the Cu/30%graphite/10%CFs composite showed TC and CTE of 453.5 Wm- 1 K- 1 and 10.9 x 10-6 K- 1, respectively. Compared to the Cu/40% graphite composite, the CTE of Cu/30%graphite/10%CFs composite was reduced by -20 % with only 4.4 % sacrifice in TC. Consequently, the Cu/graphite/CFs hybrid composites showed an excellent balance between TC and CTE, which are superior to the conventional Cu/graphite and Cu/CFs composites. The findings of this work provide new insights for designing and preparing new thermal management materials.