Reaction synthesized Al2O3-based intermetallic composites

Intermetallics-reinforced Al2O3 composites have been fabricated by reaction sintering compacts of intensively milled powder mixtures containing either metal oxides and Al or elemental metals, Al and Al2O3. During carefully controlled heal-treatment in non-oxidizing atmosphere, the metal oxides, for instance TiO2, Fe2O3 and Nb2O5, are reduced by Al to form the respective aluminides (TixAly, NbxAly). Alternatively, aluminides can also be formed through reaction between Al and elemental metals (e.g. Fe). By adding Al2O3 to the starting mixture, the intermetallic/ceramic ratio of these alumina-aluminide alloys (3A) can be adjusted within a wide range. At intermetallic volume fractions > similar to 20 vol.%, both phases are continuous, exhibiting a microstructure similar to that of products of directed metal oxidation or reactive metal penetration processes. In this paper, systems based on TixAly, FeAl and NbAl3 are emphasized. The principles of the reaction synthesis process and the influence of the processing parameters on microstructural development and mechanical properties are described. (C) 1998 Acta Metallurgica Inc.