Effects of Al content on formation of Ta 2AlC by self-propagating high-temperature synthesis

Abstract

Preparation of the ternary carbide Ta 2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from elemental powder compacts of different compositions. The synthesis reaction is characterized by a nearly planar combustion front traversing the entire sample in a self-sustaining manner. When compared with those of the reactant compact with stoichiometry of Ta:Al:C = 2:1:1, lower combustion front velocities and temperatures were observed for the samples containing more Al than the stoichiometric amount. The as-synthesized products are generally composed of Ta 2AlC as the dominant phase along with two minor carbides Ta 2C and Ta 4AlC 3, both of which can be reduced by increasing the amount of Al in the sample. On the other hand, an aluminide compound Ta 2Al was detected in the final product when the green compact contained carbon less than the stoichiometric quantity. Finally, an optimum composition arrived at Ta:Al:C = 2:1.6:1, with which the powder compact produced single-phase Ta 2AlC through SHS. The grains of Ta 2AlC are typically plate-like with a size of 5–10 μm and the layered structure consisting of closely packed Ta 2AlC is evident in the product obtained from the sample with sufficient Al. In addition, a set of possible reaction paths to produce Ta 2AlC was proposed, including the reactions of Ta 2C with Al and Ta 2Al with carbon, as well as the interaction between Ta 4AlC 3, Ta 2Al, and Al.