Nanostructured TiC1-X-TiB2 Composites Obtained by Metastability Processing

Non-oxide ceramic nanostructured powders are synthesized through metastable transformation processing based on the Self-propagating High-temperature Synthesis (SHS) process followed by quenching. Binary systems like the investigated TiC-TiB2, when quenched from the liquid state give rise to metastable structures capable of being converted into a stable, fine-grained (nanocomposite) microstructure upon recrystallization by medium temperature treatments. A necessary condition is that the combustion temperature of the SHS reaction is higher than the eutectic temperature. A previous optimisation of the reaction stoichiometry was carried out to obtain SHS products with composition approximately equal to the eutectic (i.e. 67% mol TiC0,7 - 33% mol TiB2), according to the reaction: 6Ti + B4C + 1.8C -> 4TiC(0.7) + 2TiB(2). In this work, different amounts of sodium borate (borax) were used in order to determine the optimum amount of additive to produce nanostructured TiC0.7-TiB2 composites. The morphological evolution of the powders after thermal treatment yielding re-crystallized structures demonstrates the metastability of the SHS-quench products. Therefore, the metastability process based on SHS-quench represents an extremely attractive route suitable for the achievement of nanocomposites.