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

The precipitation of interfacial carbides in a carbon fibre-reinforced aluminium alloy produced by liquid metal infiltration has been invest igated. Lath-like aluminium carbides of the type Al4C3 nucleate hetero geneously at the fibre surface and cause formation of deleterious surf ace notches. Transmission Electron Microscopy (TEM) studies showed tha t (0001) basal planes of the carbide phase preferentially form at surf ace defects constituted by small clusters of carbon layers inclined to the fibre surface, which locally expose their reactive basal plane ed ges. A crystallographic relationship in the form (0001)Al4C3 // (001)C is locally established with the fibre structure, and subsequent growt h of carbides is fast into the molten aluminium matrix along preferent ial [2110BAR] direction. It is suggested that carbides develop lath-li ke in shape mainly because their thickening at the fibre surface-is li mited by the different orientation and lower reactivity of adjacent fi bre surface regions.