In situ processing of dense Al2O3-Ti aluminide interpenetrating phase composites

Self-propagating high-temperature synthesis (SIIS) of compacted blends of nano-size TiO2 and micron-size Al powders was used to fabricate in situ alumina-TiAl/Ti3Al interpenetrating phase composites. Combustion wave propagation and pressureless or pressure-assisted thermal explosion (TE) modes have been investigated, and samples' temperature in the course of combustion synthesis has been accurately monitored. The ignition of self-sustained reaction in the system studied occurred at temperatures well above the melting point of Al, and temperature evolution in the samples was affected by interfacial barriers and by heat transfer to the surrounding ambience. The application of a moderate pressure (similar to 50 MPa) during thermal explosion at 950degreesC yielded near fully dense (up to 98% TD) Al2O3 -TiAl/Ti3Al composites with fine micron size interpenetrating ceramic and intermetallic networks. The aluminide component had a very fine submicron gamma + alpha2 lamellar microstructure. The TE procedure performed under uni-axial pressure between press rams (reactive forging) seems especially attractive due to the extremely short processing cycle (several minutes) and near-net-shape capability. This approach is compared with reactive hot pressing (RHP) where only partial conversion of reagents into products was observed after one hour exposure at 950 degreesC. (C) 2002 Elsevier Science Ltd. All rights reserved.