Effects of TiC addition on formation of Ti3SiC2 by self-propagating high-temperature synthesis

Formation of Ti3SiC2 was conducted by self-propagating high-temperature synthesis (SHS) from both the elemental powder compacts of Ti:Si:C = 3:1:2 and the TiC-containing samples compressed from powder mixtures of Ti/Si/C/TiC with TiC content ranging from 4.3 to 33.3 mol%. The effect of TiC addition was studied on combustion characteristics and the degree of phase conversion. For the elemental powder compacts, with the progress of combustion wave the sample experiences substantial deformation, including axial elongation and radial contraction. The extent of sample deformation and flame-front propagation velocity were considerably reduced for the samples with TiC addition, because the dilution effect of TiC lowered the reaction temperature. Two reaction mechanisms were adopted to explain the formation of Ti3SiC2, one involving the reaction of a Ti–Si liquid phase with solid reactants for the elemental powder compact and the other dominated by the interaction of solid-phase species for the TiC-containing sample. For all products synthesized in this study, the XRD analysis identifies formation of Ti3SiC2 along with a major impurity TiC and a small amount of Ti5Si3. The resulting Ti3SiC2 is typically elongated grains. Based upon the XRD profile, the Ti3SiC2 content at a level of 71.5 vol.% was obtained in the product from the elemental powder compact. With the addition of TiC, an improvement in the yield of Ti3SiC2 was observed and an optimal conversion reaching 85 vol.% was achieved by the sample with 20 mol% of TiC. However, further increase of the TiC amount led to a decrease in the Ti3SiC2 content, because of the low reaction temperature around 1150 °C.