Thermal properties of metal matrix composites with planar distribution of carbon fibres

Abstract

High thermal conductivity (TC) and a tunable coefficient of thermal expansion are essential properties for heat management materials operating in a wide temperature range. We combine both properties in a composite with a low-density metal matrix reinforced with pitch-based carbon fibres. The thermal conductivity of the metal matrix was increased by 50%, the thermal expansion coefficient was reduced by a factor of five. The samples were produced by powder metallurgy and have a planar random distribution of fibres, leading to high performance in two dimensions.Surface of a metal matrix composite with 50% carbon fibre (CF) strengthening (optical microscope, 20Â magnification). RapidResearch Letter 1700090 (4 of 5) V. Oddone and S. Reich: Thermal properties of metal matrix composites ß

Understanding the negative thermal expansion in planar graphite–metal composites

“…However, we still observed lower z-CTE than x,y-CTE for filler mixtures with up to 25% carbon fibers [19]. Pure carbon fibers as filler resulted in higher z-CTE and lower x,y-CTE [12].…”

“…If the different thermal expansion is not absorbed by flexible components, the induced stress will weaken the structure and may cause failure. Carbon based particles and fibers are widely used as filler in metal matrices for reducing the CTE [3,4,13,[5][6][7][8][9][10][11][12]. Carbon fibers and carbon nanotubes have a low or negative CTE along the fiber direction, graphene and graphite flakes along the crystal lattice plane.…”

Isotropic thermal expansion in anisotropic thermal management composites filled with carbon fibres and graphite

“…The TC increased in a plane perpendicular to the force direction (x,yplane) and decreased along the direction of force (z-axis). The CTE was dependent on the filler geometry: using carbon fibres as a filler we reduced the CTE in the x,y-plane down to 3 ppm K -1 [16], whereas with graphite flakes as a filler we obtained a CTE along the z-axis as low as -10 ppm K -1 [9][10][11]. The CTE reduction for carbon fibres composites is explained by the low axial CTE and high modulus of the fibres.…”

“…The degree of alignment of the fillers on the x,y-plane is dependent on the compression ratio, i.e. the ratio between the density of the powder mixture and the density of the sintered sample [16]. The structure of a sample section is visible in Fig.…”

“…However, for a direct contact the low coefficient of 2 thermal expansion (CTE) of electronic components must match the CTE of the heat sink [1][2][3], a condition that cannot be fulfilled by common metals such as copper and aluminium. Metal matrix composites with high thermal conductivity (TC) and low CTE were proposed in several research works as high performance heat sinks, mostly combining highly conducting metal matrices with graphite [4][5][6][7][8][9][10][11][12] or carbon fibres [3,[13][14][15][16] fillers, which have high TC and low CTE in a plane or along the axis.…”