ELASTIC-MODULI, THERMAL-EXPANSION AND MICROSTRUCTURE OF COPPER-MATRIX COMPOSITE REINFORCED BY CONTINUOUS GRAPHITE FIBERS

Copper-matrix composites reinforced by continuous graphite fibres (C(g)) were processed by hot-pressing layers of metallic prepregs, each fibre within the yarns having previously been coated with copper by electroplating. The electrodeposition and consolidation conditions were optimized to minimize the residual porosity, which could be considered as negligible. One-dimensional (1 D) and two-dimensional composites were obtained by this technique. In addition to the good metallurgical quality of the matrix, examination of the fibre/matrix interphase by Auger electron spectroscopy confirmed the excellent chemical compatibility between copper and graphite. As a consequence, the ultimate tensile strength of fibres extracted from the matrix remained nearly unchanged. The thermal expansion coefficients of 1 D C(g)/Cu composite materials were determined between 100 and 300-degrees-C, along the two orthogonal directions. Values ranging from 8 to 9 x 10(-6)degrees-C-1 in the composite plane and from 16 to 18 X 10(-6)-degrees-C-1 in the orthogonal direction were obtained. These results, which are related to the strong anisotropy of the ex-pitch graphite fibre, are correlated to the theoretical values found with the rule of mixtures. The poor Young's modulus and the tensile strength values are correlated to the microstructure of the fibre/matrix interphase.