Effects of shape and alignment of reinforcing graphite phases on the thermal conductivity and the coefficient of thermal expansion of graphite/copper composites

To investigate the effects of the shape and alignment of reinforcing graphite phases on the thermal conductivity (TC) and coefficient of thermal expansion (CTE) of graphite/copper (Gr/Cu) composites, test composites were fabricated using the mechanical mixing and electroless plating methods. Graphite flakes with high anisotropy and graphite granules with low anisotropy were used as the reinforcing phases, and the TC and CTE of the manufactured composites were measured in the in-plane and through-plane directions, and were compared with theoretical estimates. The present study revealed that the TC and CTE values of the Gr/Cu composites were significantly affected by the shape and alignments of the reinforcing graphite phases, and by the sizes of the graphite phases. The effects of the size of the reinforcing graphite on the TC value of the composites were more extensive than its alignment, but its alignment was a more dominant factor than its size in the determination of the CTE. Correspondingly, control of the shape, size, and alignment of the reinforcing graphite can potentially reduce the anisotropy of TC and CTE in the Gr/Cu composites.