Effects of Compositional Ratio of Ti-Al-C on Formation of Ti2AlC by Self-Sustaining Combustion Synthesis

TL;DR

Researchers studied how changing the ratios of titanium, aluminum, and carbon affects the formation of Ti2AlC through a combustion process.

Contribution

The study reveals how varying Ti-Al-C ratios influences combustion behavior and product composition during Ti2AlC synthesis.

Findings

Excess aluminum and deficient carbon improve Ti2AlC yield by forming intermediate phases like TiAl and TiC.

The optimal composition of 91.9% Ti2AlC was achieved with Ti:Al:C = 2:1.2:0.9.

Ti2AlC grains formed thin platelets with a laminated microstructure typical of MAX phases.

Abstract

The formation of Ti2AlC was investigated by self-propagating high-temperature synthesis (SHS) from the elemental Ti-Al-C powder compacts. The compositional ratios of Ti:Al:C varied from 2:1:1 to 2:1.2:0.8 to explore the effects of deficient carbon and excess Al on the combustion kinetics and product formation. For the Ti-Al-C powder compacts, self-sustaining combustion featuring a distinct combustion wave was readily achieved upon ignition. Excess Al caused a decrease in combustion temperature and flame-front velocity, while deficient carbon showed relatively little influence. The synthesized product from the sample with an exact stoichiometry of Ti:Al:C = 2:1:1 was composed of 79.5 wt.% Ti2AlC, 9.8 wt. Ti3AlC2, 10.7 wt.% TiC, and a small amount of Ti3AlC. The addition of excess Al by 20 at.% not only increased the yield of Ti2AlC but avoided the formation of Ti3AlC. A reduction of carbon further improved the evolution of Ti2AlC. The sample with an off-stoichiometric proportion of Ti:Al:C = 2:1.2:0.9 yielded the optimum product composition of 91.9 wt.% Ti2AlC, 4.2 wt.% Ti3AlC2, and 3.9 wt.% TiC. This was attributed to the fact that excess Al and deficient carbon facilitated the formation of TiAl and sub-stoichiometric TiC, both of which acted as the intermediate phases to combine into Ti2AlC. The as-synthesized Ti2AlC grains were in the shape of thin platelets with a size of 4–8 μm and a thickness of about 1.0 μm. A laminated microstructure formed by closely stacked platelets is typical of the MAX carbide.

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