The microstructures and properties of graphite flake/copper composites with high volume fractions of graphite flake

Graphite flake (average lateral size of 292 μm and average thickness of 13 μm)/copper composites with high volume fractions (72.08%-93.34 %) of graphite flake were produced by a vacuum hot pressing method. Results show that the composites are anisotropic due to the alignment of the surface plane of graphite flake perpendicular to the pressing direction. With increasing the volume fraction of graphite flake, the density of the composites decreases from 4.07 to 2.63 g cm−3, the relative density decreases apparently when the volume fraction of graphite flake are more than 82.6%, the in-plane electrical conductivity decreases from 14.71% to 2.45% of the international annealed copper standard, the in-plane coefficient of thermal expansion decreases from 6.6 to 2.2×10−6 /K, the in-plane bending strength decreases from 42.48 to 14.63 MPa, the in-plane compressive strength decreases 45.75 to 20.46 MPa while the in-plane thermal conductivity exhibits a maximum of 663.73 W m−1 K−1 at the volume fraction of GF 82.6%. The maximum in-plane thermal conductivity is caused by inter-flake pores that are not fully infiltrated by Cu. The in-plane and out-of-plane thermal conductivity agree well with the modified layers-in-parallel model and modified layers-in-series, respectively.