Use of TiH sub(2) as a reactant in combustion synthesis of porous Ti sub(5)Si sub(3) and Ti sub(5)Si sub(3)/TiAl intermetallics

Porous Ti sub(5)Si sub(3) and Ti sub(5)Si sub(3)/TiAl intermetallics were fabricated by self-propagating high-temperature synthesis (SHS) from elemental powder compacts with addition of TiH sub(2). The TiH sub(2) content ranged from 1.25 to 6.25 mol.% for formation of the Ti sub(5)Si sub(3) monoliths and from 2 to 10 mol.% for the Ti sub(5)Si sub(3)/TiAl composites. Due to endothermic decomposition of TiH sub(2), the increase of TiH sub(2) decreased the reaction temperature and combustion wave velocity. Moreover, dehydrogenation of TiH sub(2) released hydrogen gas to act as a pore-forming agent and generated highly reactive Ti to facilitate the reaction. The porosity of the intermetallic product increased with increasing TiH sub(2) content and the microstructure with a uniform distribution of pores was attained. As a consequence, the porosity of as-synthesized Ti sub(5)Si sub(3) monoliths was controllable and increased from 38% to 60% with TiH sub(2) additions. Likewise, Ti sub(5)Si sub(3)/TiAl composites with an increasing porosity from 31% to 56% were obtained from the TiH sub(2)-added samples.