Intermetallic/Ceramic Composites Synthesized from Al-Ni-Ti Combustion with B4C Addition

The fabrication of intermetallic/ceramic composites by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) was investigated in the Al-Ni-Ti system with the addition of B4C. Two reaction systems were employed: one was used to produce the composites of xNiAl-2TiB(2)-TiC with x = 2-7, and the other was used to synthesize yNi(3)Al-2TiB(2)-TiC with y = 2-7. The reaction mechanism of the Al-Ni-Ti system was strongly influenced by the presence of B4C. The reaction of B4C with Ti was highly exothermic, so the reaction temperature and combustion velocity decreased due to increasing levels of Ni and Al in the reactant mixture. The activation energies ofE(a)= 110.6 and 172.1 kJ/mol were obtained for the fabrication of NiAl- and Ni3Al-based composites, respectively, by the SHS reaction. The XRD (X-ray diffraction) analysis showed an in situ formation of intermetallic (NiAl and Ni3Al) and ceramic phases (TiB(2)and TiC) and confirmed no reactions taking place between Ti and Al or Ni. The microstructure of the product revealed large NiAl and Ni3Al grains and small TiB(2)and TiC particles. With the addition of TiB(2)and TiC, the hardness of NiAl and Ni3Al was considerably increased and the toughness was also improved.