Combustion synthesis of TiN–Ti silicide and TiN–Si 3N 4 composites from Ti–Si 3N 4 powder compacts in Ar and N 2

Abstract

Preparation of the TiN–Ti silicide and TiN–Si 3N 4 composites was conducted by solid-state and solid–gas combustion of the Ti–Si 3N 4 powder compacts in Ar and N 2, respectively. Effects of the sample stoichiometry on combustion characteristics and product compositions were studied. The dual roles played by Si 3N 4 in these two synthesis routes were investigated; that is, Si 3N 4 serves as a reactant in formation of the TiN–Ti silicide composite, but it is inert when producing the TiN–Si 3N 4 composite. For the samples with a molar ratio of Ti/Si 3N 4 between 4.0 and 9.0, the solid-state reaction with a self-sustaining combustion wave was achieved under Ar and final products were the composite materials of TiN with TiSi 2 and/or Ti 5Si 3. The increase of the Ti content in the reactant mixture facilitated formation of the Ti-rich silicide Ti 5Si 3, which enhanced the reaction exothermicity and led to an improvement in the phase conversion. As a result, the TiN–Ti 5Si 3 composites were obtained from the samples with Ti/Si 3N 4 = 7.75 and 9.0. On the other hand, the powder compact of Ti/Si 3N 4 = 3.0 was adopted to prepare the TiN–Si 3N 4 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 Si 3N 4 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 Si 3N 4, thus resulting in formation of the TiN–Si 3N 4 composite free of impurities.