REACTION SYNTHESIZED AL2O3-BASED INTERMETALLIC COMPOSITES

Intermetallics-reinforced Al2O3 composites have been fabricated by rea ction sintering compacts of intensively milled powder mixtures contain ing either metal oxides and Al or elemental metals, Al and Al2O3. Duri ng carefully controlled heal-treatment in non-oxidizing atmosphere, th e metal oxides, for instance TiO2, Fe2O3 and Nb2O5, are reduced by Al to form the respective aluminides (TixAly, NbxAly). Alternatively, alu minides can also be formed through reaction between Al and elemental m etals (e.g. Fe). By adding Al2O3 to the starting mixture, the intermet allic/ceramic ratio of these alumina-aluminide alloys (3A) can be adju sted within a wide range. At intermetallic volume fractions > similar to 20 vol.%, both phases are continuous, exhibiting a microstructure s imilar to that of products of directed metal oxidation or reactive met al penetration processes. In this paper, systems based on TixAly, FeAl and NbAl3 are emphasized. The principles of the reaction synthesis pr ocess and the influence of the processing parameters on microstructura l development and mechanical properties are described. (C) 1998 Acta M etallurgica Inc.