Effects of using Al4C3 as a reactant on formation of Ti3AlC2 by combustion synthesis in SHS mode

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 Al4C3-containing samples compressed from the powder mixtures of Ti/Al/C/Al4C3 with Al4C3 content ranging from 1.85 to 5.56 mol%. The reactant compact with 5.56 mol% Al4C3 represents a composition of 3Ti + 1.25C + 0.25Al4C3, within which Al4C3 serves as the only source of Al. Effects of the Al4C3 addition and sample green density were studied on the combustion characteristics and product compositions. Due to formation of liquid Ti–Al melt and growth of the Ti3AlC2 grains, the powder compact was subjected to substantial deformation during the SHS process. With an increase in the Al4C3 content, the reaction temperature and flame-front propagation velocity were reduced, but the degree of Ti3AlC2 formation was improved. In addition to Ti3AlC2 formed as the dominant phase, the XRD analysis identified two secondary phases TiC and Ti2AlC in the synthesized products. Formation of Ti3AlC2 was also enhanced by increasing the sample green density. For the elemental powder compacts, the content of Ti3AlC2 yielded in the products increased from 50.5 to 73.2 wt% with increasing sample density from 45 to 65% TMD. It was found that under a constant compaction density of 60% TMD, the product composed of 75.3 wt% Ti3AlC2 was produced from the 5.56 mol% Al4C3-containing sample, in comparison with only 61 wt% Ti3AlC2 from the elemental reactant. Moreover, as the sample density further increased to 70% TMD, the yield of Ti3AlC2 approaching 80 wt% was obtained.