In situ formation of TiB2/TiC and TiB2/TiN reinforced NiAl by self-propagating combustion synthesis

Fabrication of TiB2/TiC- and TiB2/TiN-reinforced NiAl in situ composites was studied by self-propagating high-temperature synthesis (SHS). The 3Ti + B4C and 3Ti + 2BN reactions were incorporated into the Ni-Al combustion system to produce ceramic phases with resultant compositions of 2TiB2 + TiC and TiB2 + 2TiN. Combustion synthesis of the TiB2/TiC-added NiAl composite is more energetic. The combustion exothermicity was reduced by increasing NiAl content. Based upon the dependence of flame-front velocity on combustion temperature, the activation energies of in situ formation of TiB2/TiC- and TiB2/TiN-added NiAl composites by solid-state combustion were determined to be 102.5 and 133.4 kJ/mol. With the decrease of NiAl from 70 to 40 mol% in the composites, the fracture toughness increases from 4.2 to 5.8 MPa m1/2 for the TiB2/TiC-added composites and in the range of 3.86-5.5 MPa m1/2 for the composites reinforced by TiB2 and TiN.