FILAMENTARY PREFORMS OF AL-13 WT-PERCENT SI ALLOY REINFORCED WITH TIC-COATED AND PRETREATED CARBON-FIBERS

Filamentary preforms of aluminium-13 wt % Si alloy reinforced with TiC -coated carbon fibres were obtained by liquid metal infiltration using K2ZrF6 as wetting agent. The interfacial structure was investigated u sing analytical electron microscopy (TEM, SEM) and the fibre strength measured following each step of processing. The reaction between the K 2ZrF6 deposit and the molten alloy is discussed on the basis of the re action products formed at the fibre-matrix interface, which mainly con sisted of fluoride compounds (K3AlF6), different zirconium-rich silici des (Si2Zr, SiZr (Al), (Al, Si)(2)Zr) and crystalline gamma-alumina. L arge amounts and/or inhomogeneous distributions of the K2ZrF6 deposit should be avoided, because the massive precipitation of colonies of in termetallics around fibres is conducive for the formation of harmful a luminium carbides and favours brittle fracture of the composite. The u tilization of TiC-coatings formed by the reactive chemical vapour depo sition process gave satisfactory results, both in terms of composite e laboration and fibre protection during liquid infiltration.