Formation of Ti3AlC2/Al2O3 and Ti2AlC/Al2O3 composites by combustion synthesis in Ti-Al-C-TiO2 systems

Preparation of Ti3AlC2/Al2O3 and Ti2AlC/Al2O3 in situ composites was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS). The SHS process incorporates the thermite reaction of Al with TiO2 into solid state combustion of the Ti-Al-C system. The extent of thermite reaction involved in the SHS process was studied on the product composition and combustion behavior. It was found that for the formation of Al2O3, the addition of the Al-TiO2 displacement reaction into the Ti-Al-C combustion system significantly reduced the flame propagation velocity and combustion temperature, both of which decreased with increasing content of Al2O3 formed in the composites. In situ formation of Al2O3 and Ti3AlC2 or Ti2AlC was confirmed by XRD analyses. Moreover, the secondary phase TiC present along with formation of Ti3AlC and Ti2AlC was reduced when the thermite reaction was involved, implying an improvement in the evolution of ternary carbides. The maximum contents of Al2O3 formed in the Ti3AlC2 and Ti2AlC-matrix composites are up to 60 and 50 mol%, respectively, beyond which the synthesis reaction cannot proceed in a self-sustaining manner due to lack of sufficient reaction exothermicity. SEM micrographs of the synthesized composites show plate-like grains packed in a laminated structure typical of Ti3AlC2 and Ti2AlC.