Copper coating on carbon fibres and their composites with aluminium matrix

Abstract

A uniform and continuous coating of copper was given to carbon fibres by cementation or electroless techniques. In both cases, when coating thicknesses were less than 0.2 μm, copper deposition was discontinuous over the fibres, and above 0.2 μm, coatings were continuous. In electroless coating, about 75% of the continuously coated fibres had a coating thickness range 0.2–0.5 μm and above this showed isolated dendrite deposits of copper. In the cementation process, about 75% of the continuously coated fibres had a coating thickness range 0.2–0.6 μm, and above this thickness, fine crystallite-type copper deposition was found over smoothly coated copper. The ultimate tensile strength of continuously electroless-coated fibres were nearer to the uncoated fibres, suggesting defect-free coating, while fibres coated by the cementation process exhibited lower ultimate tensile strength values. The tensile fracture of both electroless- and cementation-coated fibres showed delamination of the coating, suggesting poor bonding between coating and the fibre. In composites, prepared by dispersing the coated chopped fibres in a pure aluminium matrix, uniform and random distribution of the fibres were observed without appreciable fibre-metal interaction. The CuAl₂ intermetallics were largely found in the matrix and only very small amounts were observed at fibre/matrix interfaces. Additions of about 2 wt% Mg to the matrix prior to the fibre dispersion did not appreciably change the distribution pattern of the fibres, but in addition to CuAl₂ phase, Mg₂Si phases were observed in the matrix as well as at the interface.