Effects of TiC and Al4C3 addition on combustion synthesis of Ti2AlC

Preparation of the ternary carbide Ti2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from the elemental powder compacts of Ti:Al:C =2:1:1, TiC-containing samples with TiC of 6.67-14.3mol%, and Al4C3-containing samples with Al4C3 of 1.96-10 mol%. Effects of TiC and Al4C3 addition were studied on combustion characteristics and the degree of phase conversion. Due to the growth of laminated Ti2AlC grains, the reactant compact was subjected to an axial elongation during the SHS process. Because the addition of TiC and Al4C3 led to a decrease in the reaction temperature, the flame-front propagation velocity was correspondingly reduced for the TiC- and Al4C3-containing samples when compared with the elemental reactants. Based upon the XRD analysis, formation of Ti2AlC along with a secondary phase TiC was identified in the synthesized products. The grains of Ti2AlC are typically plate-like with a size of 10-20 mu m and several laminated Ti2AlC grains form a layered structure. The content of Ti2AlC yielded from the elemental powder compacts is about 85 wt%. The addition of TiC was found to facilitate the formation mechanism and therefore to enhance the extent of Ti2AlC conversion approaching 90 wt%. As a result of the reduced exothermicity of the reaction, however, the content of Ti2AlC decreased slightly in the products synthesized from the Al4C3-added samples. (C) 2008 Elsevier B.V. All rights reserved.