INFLUENCE OF MICROSTRUCTURE ON THE STRENGTH OF NICALON-REINFORCED ALUMINUM METAL-MATRIX COMPOSITES

The microstructure and mechanical properties of two aluminium-based co mposites reinforced with Nicalon fibre are investigated. During compos ite processing, aluminium carbide forms at the interface as a result o f a reaction between aluminium and free Magnesium, when present in the aluminium matrix, diffuses into the outer (approximately 200 nm) laye r of the fibre where it reacts with the silicon oxycarbide constituent to form magnesium-containing oxide and also to free carbon for the pr oduction of more interfacial aluminium carbide. These chemical reactio ns affect to differing degrees the strength of a fibre, as measured af ter extraction from the two composites, and influence the respective f ibre/matrix interfacial friction stress and composite strength. A simp le rule-of-mixtures approach based upon the measured strength of extra cted fibres gave some agreement with longitudinal properties of the co mposite, but treatment of the fibres as bundles, using a Weibull proba bility distribution of properties, provided more accurate predictions.