Formation of TiAl–Ti2AlC in situ composites by combustion synthesis

Preparation of TiAl–Ti2AlC in situ composites with a broad range of composition was conducted by self-propagating high-temperature synthesis (SHS) with compressed samples from the mixture of elemental powders. When compared with SHS formation of monolithic TiAl, the addition of carbon particles to the Ti–Al powder mixture enhances the sustainability of the reaction. It was found that no prior heating was required for the samples prepared to produce the composites containing more than 20 mol% Ti2AlC, in contrast to the need of preheating at 200 °C for single-phase TiAl formation. This is attributed to the fact that formation of Ti2AlC is more exothermic than that of TiAl. As a result, the combustion temperature and combustion wave velocity increase with the content of Ti2AlC formed in the TiAl–Ti2AlC composite, and approach the values associated with formation of single-phase Ti2AlC when considerable amounts of Ti2AlC are yielded. The XRD analysis of the end products confirms formation of TiAl–Ti2AlC in situ composites. Moreover, simultaneous formation of Ti2AlC promotes the phase evolution of the aluminide compounds. That is, the secondary aluminide phase, Ti3Al, was no longer detected in the TiAl–matrix composites containing Ti2AlC of 30 mol% or above.