Effects of TiC, TiH₂, Al, and Carbon on Production of Ti₃AlC₂ by Self-Sustaining Combustion Synthesis

The production of Ti₃AlC₂ was investigated by self-propagating high-temperature synthesis (SHS) using the sample compacts composed of elemental powders with or without TiC and TiH₂ additions. The influence of Al, carbon, TiC, and TiH₂ was explored on the combustion sustainability, combustion velocity and temperature, and phase composition and microstructure of the product. The experimental results indicated that the elemental sample with an Al-excess composition increased the combustion velocity and improved the formation of Ti₃AlC₂, but the sample with a carbon-deficient composition produced the opposite effect. Although both TiC and TiH₂ additions decreased combustion exothermicity, an appropriate amount of TiC enhanced the yield of Ti₃AlC₂. However, the incomplete decomposition made TiH₂ unsuitable as a source of Ti and resulted in a low yield of Ti₃AlC₂. In this study, the final product containing the highest content of Ti₃AlC₂ was synthesized from the Al-excess and TiC-added sample of 2.5Ti + 1.2Al + 1.5C + 0.5TiC, and the product was composed of 89.3 wt.% Ti₃AlC₂, 5.9 wt.% Ti₂AlC, and 4.8 wt.% TiC. A reaction mechanism was proposed for the formation of Ti₃AlC₂ by SHS, which involved three exothermic reaction steps sequentially producing TiC, Ti₂AlC, and Ti₃AlC₂. The as-synthesized Ti₃AlC₂ grains were in the shape of thin platelets with a thickness of about 1.0 μm, and a layered structure formed by closely stacked platelets was clearly observed.