Combustion synthesis of Ti3AlC2 from Ti/Al/C/TiC powder compacts

Preparation of the ternary carbide Ti3AlC2 was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from both the elemental powder compacts of Ti:Al:C = 3:1:2 and the TiC-containing samples compressed from the powder mixtures of Ti/Al/C/TiC with TiC content ranging from 4.35 to 26.3 mol%. The effect of TiC addition was studied on combustion characteristics and the degree of phase conversion. For the elemental reactants, the powder compact experiences substantial deformation during the SHS process, including axial elongation and radial contraction. Because the addition of TiC lowered the reaction temperature, the extent of sample deformation and flame-front propagation velocity were considerably reduced for the TiC-containing samples. Based upon the XRD analysis, formation of Ti3AlC2 along with two secondary phases TiC and Ti2AlC was identified in the synthesized products. The grains of Ti3AlC2 are typically plate-like with a size of 5–10 μm. The content of Ti3AlC2 yielded increases with sample green density for the elemental powder compacts, resulting in the mass fraction of Ti3AlC2 increasing from 50.5 to 73.2% in the products with respect to the increase of relative density of the sample from 45 to 65%. The improvement in formation of Ti3AlC2 was also made by properly adding TiC in the reactant compact. An optimal conversion yielding a product with mole fractions of 84.6% Ti3AlC2, 9.8% TiC, and 5.6% Ti2AlC was achieved by the sample composed initially of 20 mol% TiC. However, further increase of the TiC amount led to a decrease in the Ti3AlC2 content, because of reduced exothermicity of the reaction.