Reaction mechanism in self-propagating high temperature synthesis of TiC-TiB2/Al composites from an Al-Ti-B4C system

The reaction sequence and phase formation mechanism in self-propagating high temperature synthesis (SHS) processing of the Al–Ti–B4C compacts were explored through a delicate microstructure and phase analysis on the combustion-wave quenched samples in combination with differential thermal analysis. The reaction sequence could be described as Al +Ti + B4C → TiAl3 + Ti + B4C → TiAln + B4C → TiAln + B13C2 + TiCx + TiaAlbCc → TiAln + TiCx + TiB2 + TiaAlbCc → Al + TiCx + TiB2. The phase formation mechanism could be ascribed to the displacive reaction between B4C and the Ti–Al melt and is essentially dependent on the dissociation and diffusion rates of carbon and boron from the B4C crystal. The reasons for the prior formation of TiCx over TiB2 and the separated residence of the TiCx and TiB2 grains in the microstructure were addressed.