LPCVD SiC COATINGS ON UNIDIRECTIONAL CARBON FIBRE-YARNS : APPLICATION TO ALUMINIUM MATRIX COMPOSITES

SiC has been chosen as a diffusion barrier in carbon/aluminium metal matrix composites. P55 carbon tows are coated with a thin SiC layer applied in a continuous LPCVD process from a Si(CH3)4-H2 mixture, using a hot wall reactor. Deposition parameters (temperature, pressure, flow rates of reactants, fibres passing rate) are determined in order to ensure a good compromise between a thorough infiltration of the yarn and the carbon amount in the SiC. The coatings on the fibres are characterized in two ways : direct observation and evaluation of the coating thickness on metallographic cross sections of a mounted tow ; determination of the composition and thickness of the layer by EPMA on isolated fibres. Coated fibres are included in an aluminium matrix and a composite is fabricated by liquid phase hot pressing : the effect of the coating is observed and discussed. An optimization of the CVD infiltration parameters is still necessary to reduce the variations in coating thickness between the core of the yarn and the external fibres