Combustion synthesis of TiN-Ti silicide and TiN-Si3N4 composites from Ti-Si3N4 powder compacts in Ar and N2

Preparation of the TiN-Ti silicide and TiN-Si3N4 composites was conducted by solid-state and solid-gas combustion of the Ti-Si3N4 powder compacts in At and N-2, respectively. Effects of the sample stoichiometry on combustion characteristics and product compositions were studied. The dual roles played by Si3N4 in these two synthesis routes were investigated; that is, Si3N4 serves as a reactant in formation of the TiN-Ti silicide composite, but it is inert when producing the TiN-Si3N4 composite. For the samples with a molar ratio of Ti/Si3N4 between 4.0 and 9.0, the solid-state reaction with a self-sustaining combustion wave was achieved under At and final products were the composite materials of TiN with TiSi2 and/or Ti5Si3. The increase of the Ti content in the reactant mixture facilitated formation of the Ti-rich silicide Ti5Si3, which enhanced the reaction exothermicity and led to an improvement in the phase conversion. As a result, the TiN-Ti5Si3 composites were obtained from the samples with Ti/Si3N4 = 7.75 and 9.0. On the other hand, the powder compact of Ti/Si3O4 = 3.0 was adopted to prepare the TiN-Si3N4 composite through solid-gas combustion under nitrogen of 0.45-1.82 MPa. It was found that the reaction of Ti with nitrogen was exothermic enough to sustain the combustion front in a self-propagating manner, during which Si3N4 acted as an inert diluent. The increase of nitrogen pressure contributed to a higher degree of nitridation. A nitrogen pressure as high as 1.48 MPa was required to achieve complete nitridation of Ti and to prevent Ti from reacting with Si3N4, thus resulting in formation of the TiN-Si3N4 composite free of impurities. (C) 2009 Elsevier B.V. All rights reserved.