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, Ga as an additive to Al–C has a detrimental effect on the reaction, which was also predicted by the theoretical calculations.