Chemically and mechanically activated combustion synthesis of B_4C-TiB_2 composites

摘要

The self-propagating high-temperature synthesis (SHS) of B_4C-TiB_2 composite powders (1:1 molar ratio) from elemental reactants is performed using polytetrafluoroethylene as reaction promoter. A threshold amount of the polymer has to be added to the mixture for establishing and sustaining the combustion front. However, due to the carburizing role played by Teflon, the resulting product also contains residual C and TiC. When initial graphite is gradually replaced by the polymer, mixture reactivity is enhanced and secondary phases correspondingly decrease, thus leading to the desired composition when all stoichiometric carbon was provided by Teflon. Furthermore, a 3 h ball milling treatment of the reactants mixture allows us to decrease the required amount of Teflon from 30 to 18 wt.%.Therefore, the combination of mechanical and chemical activating methods provides a useful tool to overcome the thermodynamic or kinetic limitations encountered during the fabrication of B_4C-TiB_2 composites by SHS.