The influence of a third element on the interface reactions in metal-matrix composites (MMC): Al-graphite system

The basic concept of achieving reduced reactions at a matrix-fiber interface by decreasing fiber solubility in the matrix of a metal matrix composite (MMC) was implemented on the Al-graphite system. Alloying the matrix of the Al-C system with small amounts of additional constituent can do this. According to theoretical calculations, Si should be the most effective constituent to reduce the reactions in the binary Al-C system. Small quantities of Si added to Al-C are effective both in decreasing C solubility in the Al matrix and limiting the formation of Al4C3 by reducing interface reactions. Fe or Ga additives should not reduce interface reactions at the matrix-fiber interface of this system, but rather augment them, leading to accelerated deterioration. Experiments were carried out on the Al-C MMC system with and without the addition of a third component. The theoretical calculations were verified by the experimental results. In the absence of Si in the Al-C MMC, the reactions at the fiber-matrix interface occur at a rapid rate with an activation energy of 62 kJ mol(-1). The kinetics of degradation of the fiber in the Al-C is discussed. Si limits such reactions. Ga as an additive to Al-C provided further substantiation of the validity of the theory. According to our experimental results, Ca as an additive to Al-C has a detrimental effect on the reaction, which was also predicted by the theoretical calculations. (C) 2000 Elsevier Science S.A. All rights reserved.