Thermal cycling behaviour of carbon fibre reinforced Cu-matrix composites

Carbon fibre reinforced copper matrix composites (CFR-Cu) combine both - properties of copper, such as excellent thermal and electrical conductivity, but also properties of the carbon fibre, e.g. a small thermal expansion coefficient. Since the desirable mix of properties is obtained by selecting the amount and type of carbon fibres, such CFR-Cu composites could serve as heat sink in electric and electronic application. The properties of CFR-Cu have been reported in previous papers. This paper is focusing on the stability of the composites against thermal cycling. The copper's coefficient of thermal expansion (CTE) is +16x10-6 /K, whereas carbon fibres typically have a negative CTE (about -1x10-6 /K). This difference in CTE may influence the interface during thermal cycling. The investigated CFR-Cu include composites with short and long, PAN and PITCH type carbon fibres. It is shown that both, fibre type and temperature interval of the thermal cycles, are of importance. The atmosphere's influence has also been investigated. CFR-Cu with short PITCH type carbon fibres are more sensitive to thermal cycling. The reason is the different surface of PITCH-type and PAN-type fibres. If the upper temperature of the thermal cycles does not exceed 155 °C there are no considerable changes of the thermo-physical properties (thermal conductivity, coefficient of thermal expansion) for all types of fibres.