Copper matrix±carbon fibre composites

Copper matrix-carbon fibre composite utilises the properties of its components: high thermal conductivity of copper and negative coefficient of thermal expansion, low density and high thermal conductivity (of several kinds) of carbon fibres. Three ways of Cu-CF composites processing (infiltration of carbon fibres by liquid copper, powder metallurgy and coating of carbon fibres by copper followed by diffusion bonding) are briefly reviewed, emphasising the third method where T 300 carbon fibres were used. General formulae for thermal expansion, thermal conductivity and Young's modulus are given. Thermal expansion and thermal conductivity of variously arranged fibres (unidirectional, cross-ply, woven, spiral) composites were measured. Unidirectional samples showed very anisotropic properties in direction along and normal to the fibres. Longitudinal CTE from 7 to 4 x 10-6/K can be achieved for 40-60 vol.% of carbon fibres. In transverse direction CTE exceeds that of copper. Longitudinal thermal conductivity is more than 50% higher than in transverse direction and decreases from ca. 200 to 150 W/mK with increasing fibre content (40-60%). Transverse thermal conductivity decreases from ca. 120 to 50 W/mK for the same volume fraction of carbon fibre. Cross-ply and woven samples showed homogeneous properties (CTE and conductivity) in two directions (in the plane of fibres) which are similar to that of the unidirectional samples in the fibre direction.