GROWTH STAGE KINETICS IN THE SYNTHESIS OF AL2O3 AL COMPOSITES BY DIRECTED OXIDATION OF AL-MG AND AL-MG-SI ALLOYS/

Although synthesis of ceramic matrix composites by the directed oxidat ion process offers significant advantages over traditional composite p rocessing routes, the scientific basis for the process is not fully un derstood. This paper is addressed to understanding the mechanism of co mposite growth from Al-Mg and Al-Mg-Si alloys theoretically and experi mentally. Analysis of the oxidation kinetics of Al-Mg and Al-Mg-Si all oys for various oxygen pressures, temperatures and durations of oxidat ion, obtained in this study and reported in the literature, demonstrat es that the growth kinetics van be tailored by the control of alloy co mposition. For the Al-Mg alloys, transport of oxygen through a thin al loy layer near the surface controls the growth rate. When Si is added to the alloy, the oxidation mechanism is completely changed. The rate of oxidation of Al-Mg-Si alloys depends on the transport of electronic species through a thin MgO layer at the top surface of the composite. Apart from contributing to a more complete understanding of the growt h stage, the mechanism of composite growth will serve as a basis for i mproving growth rates. (C) 1996 Elsevier Science Limited