Thermophysical properties and microstructure of short carbon fibre reinforced Cu-matrix composites made by electroless copper coating or powder metallurgical route respectively

Abstract

C fibre reinforced Cu matrix composites have the interesting properties of Cu, i.e. thermal and electrical conductivities, but the properties of the C fibre, i.e. small CTE, dominate mechanical behaviour. As desired composite properties can be obtained by selecting the amount and type of C fibres, it is suitable for electronic applications such as special heat sinks. Cu matrix composites with high conducting short fibres are a promising research field. Short C fibre reinforced Cu composites were made by hot-pressing of Cu coated C fibres chopped into different lengths (60 /spl mu/m-2 mm). By using electroless Cu coating-based production, a good fibre distribution in the matrix and good interfacial contact were obtained. The fibre length distribution strongly influences composite properties. During hot pressing, the C fibres take on a preferred orientation in a plane perpendicular to the hot pressing direction. Within this plane, fibre orientation is random. C fibre volume content was varied in a 38-64 vol.% range. The composite microstructures were studied by SEM and optical microscopy. Measured thermal conductivity and CTE were compared with microstructural results and results from mathematical models. The composites have thermal conductivity of about 250-300 W/mK in two dimensions and about 140 W/mK in the third dimension. The CTE can be tailored in a range of 4-10 ppm/K by changing the C fibre content. The relatively low density of 4-6 g/cm/sup 3/ is also important where weight reduction is desired. The results are compared with composites produced by powder metallurgical methods and those made with low conducting short C fibres.