On the role of brittle interfacial phases on the mechanical properties of carbon fibre reinforced Al-based matrix composites

High-resolution microfractography performed in combination with transmission electron microscopy shows that the mechanical behaviour of carbon fibre reinforced Al-based matrix composites is related to the presence of brittle interfacial phases. Attaining the required specifications in the unreinforced part of cast aluminium aeronautical components locally reinforced with a carbon preform necessitates the use of a highly alloyed Al-based matrix. Moreover, the precipitate hardening heat treatment appropriate to the unreinforced alloy must be applied to the whole component. The two composites M40J/A357 and M40J/C-pyr/A357 (pyrolytic carbon coated fibres), either as-cast or after the usual T6 heat treatment of the A357 alloy (16 h solution treatment at 540 degrees C followed by water quenching and 6 h ageing at 160 degrees C) have been investigated. The formation of Si and Al4C3 interfacial brittle phases resulting from both the dendritic solidification and the solution treatment leads to the premature failure of the composite. (C) 1999 Elsevier Science S.A. All rights reserved.