ON THE FORMATION OF INTERFACIAL CARBIDES IN A CARBON-FIBER-REINFORCED ALUMINUM COMPOSITE

The precipitation of interfacial carbides in a carbon fibre-reinforced aluminium alloy produced by liquid metal infiltration has been investigated. Lath-like aluminium carbides of the type Al4C3 nucleate heterogeneously at the fibre surface and cause formation of deleterious surface notches. Transmission Electron Microscopy (TEM) studies showed that (0001) basal planes of the carbide phase preferentially form at surface defects constituted by small clusters of carbon layers inclined to the fibre surface, which locally expose their reactive basal plane edges. A crystallographic relationship in the form (0001)Al4C3 // (001)C is locally established with the fibre structure, and subsequent growth of carbides is fast into the molten aluminium matrix along preferential [2110BAR] direction. It is suggested that carbides develop lath-like in shape mainly because their thickening at the fibre surface-is limited by the different orientation and lower reactivity of adjacent fibre surface regions.