Formation of TiB2-MgAl2O4 Composites by SHS Metallurgy.

Abstract

TiB2-MgAl2O4 composites were fabricated by combustion synthesis involving metallothermic reduction reactions. Thermite reagents contained Al and Mg as dual reductants and TiO2 or B2O3 as the oxidant. The reactant mixtures also comprised elemental Ti and boron, as well as a small amount of Al2O3 or MgO to serve as the combustion moderator. Four reaction systems were conducted and all of them were exothermic enough to proceed in the mode of self-propagating high-temperature synthesis (SHS). The reaction based on B2O3/Al/Mg thermite and diluted with MgO was the most exothermic, while that containing TiO2/Al/Mg thermite and Al2O3 as the diluent was the least. Depending on different thermites and diluents, the combustion front temperatures in a range from 1320 to 1720 °C, and combustion wave velocity from 3.9 to 5.7 mm/s were measured. The XRD spectra confirmed in situ formation of TiB2 and MgAl2O4. It is believed that MgAl2O4 was synthesized through a combination reaction between Al2O3 and MgO, both of which can be totally or partially produced from the metallothermic reduction of B2O3 or TiO2. The microstructure of the TiB2-MgAl2O4 composite exhibited fine TiB2 crystals surrounded by large densified MgAl2O4 grains. This study demonstrated an energy-saving and efficient route for fabricating MgAl2O4-containing composites.