Formation of Ti 3AlC 2/Al 2O 3 and Ti 2AlC/Al 2O 3 composites by combustion synthesis in Ti–Al–C–TiO 2 systems

Abstract

Preparation of Ti 3AlC 2/Al 2O 3 and Ti 2AlC/Al 2O 3 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 TiO 2 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 Al 2O 3, the addition of the Al–TiO 2 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 Al 2O 3 formed in the composites. In situ formation of Al 2O 3 and Ti 3AlC 2 or Ti 2AlC was confirmed by XRD analyses. Moreover, the secondary phase TiC present along with formation of Ti 3AlC and Ti 2AlC was reduced when the thermite reaction was involved, implying an improvement in the evolution of ternary carbides. The maximum contents of Al 2O 3 formed in the Ti 3AlC 2 and Ti 2AlC-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 Ti 3AlC 2 and Ti 2AlC.