Effects of using Al 4C 3 as a reactant on formation of Ti 3AlC 2 by combustion synthesis in SHS mode

Abstract

Preparation of the ternary carbide Ti 3AlC 2 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 Al 4C 3-containing samples compressed from the powder mixtures of Ti/Al/C/Al 4C 3 with Al 4C 3 content ranging from 1.85 to 5.56 mol%. The reactant compact with 5.56 mol% Al 4C 3 represents a composition of 3Ti + 1.25C + 0.25Al 4C 3, within which Al 4C 3 serves as the only source of Al. Effects of the Al 4C 3 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 Ti 3AlC 2 grains, the powder compact was subjected to substantial deformation during the SHS process. With an increase in the Al 4C 3 content, the reaction temperature and flame-front propagation velocity were reduced, but the degree of Ti 3AlC 2 formation was improved. In addition to Ti 3AlC 2 formed as the dominant phase, the XRD analysis identified two secondary phases TiC and Ti 2AlC in the synthesized products. Formation of Ti 3AlC 2 was also enhanced by increasing the sample green density. For the elemental powder compacts, the content of Ti 3AlC 2 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% Ti 3AlC 2 was produced from the 5.56 mol% Al 4C 3-containing sample, in comparison with only 61 wt% Ti 3AlC 2 from the elemental reactant. Moreover, as the sample density further increased to 70% TMD, the yield of Ti 3AlC 2 approaching 80 wt% was obtained.