Effects of TiC and TiN addition on combustion synthesis of Ti2AlC0.5N0.5 solid solutions

Preparation of the solid solution Ti2AlC0.5N0.5 was investigated by self-propagating high-temperature synthesis (SHS) from TiC- and TiN-diluted powder compacts. For the TiC-added samples, combustion reaction was conducted in gaseous nitrogen of 0.45–1.82 MPa. The increase of nitrogen pressure augments the combustion temperature and thus accelerates the reaction front. However, the phase composition of the synthesized product is not affected by the variation of nitrogen pressure, indicating the formation of Ti2AlC0.5N0.5 and three minor phases TiC, TiN, and Ti3Al. For the TiN-containing samples of insufficient nitrogen, the SHS reaction was performed in nitrogen of 0.45 MPa, showing that the increase of the TiN content reduced the combustion temperature and flame-front velocity. Moreover, combustion of the TiN-diluted samples in nitrogen often caused excessive nitridation of the powder compacts. As a result, Ti2AlC0.5N0.5 was yielded along with a substantial amount of secondary phases, including TiN, TiC, and AlN. On the other hand, solid state combustion in Ar was applied for the TiN-added sample at the exact stoichiometry of Ti2AlC0.5N0.5. When compared with combustion synthesis involving gaseous nitrogen, a better phase conversion was achieved by solid state combustion, which produced Ti2AlC0.5N0.5 with negligible amounts of TiC and TiN.