An investigation on formation of Nb2AlC by combustion synthesis of Nb2O5–Al–Al4C3 powder compacts

Abstract

Abstract Preparation of layered ternary carbide Nb2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from Nb2O5–Al–Al4C3 powder compacts. Effects of the contents of Al and Al4C3 on the product composition and combustion behavior were studied by adopting two series of sample stoichiometries with Nb2O5:Al:Al4C3 varying from 3:9:1 to 3:13:1 (for supplying additional Al) and 3:9:1 to 3:9:1.6 (for additional Al4C3). When compared with the powder compact of Nb2O5:Al:Al4C3 = 3:9:1, the increase of Al or Al4C3 lowered the combustion temperature and thus decelerated the combustion front. However, the formation of Nb2AlC was effectively improved by the samples containing an appropriate amount of additional Al or Al4C3. In this study, the optimum evolution of Nb2AlC was obtained from the powder compacts with proportions of Nb2O5:Al:Al4C3 = 3:11:1 and 3:9:1.1. Besides Nb2AlC and Al2O3, the binary carbide NbC was always present in the final products. A further increase in Al or Al4C3 led to the formation of Nb4AlC3 and NbAl3, and the amount of NbC increased noticeably as the content of Al4C3 was excessive. As a result, for the samples with relatively high contents of Al4C3, like Nb2O5:Al:Al4C3 = 3:9:1.5 and 3:9:1.6, NbC was found to be the only carbide in the final products. The as-synthesized Nb2AlC grains are typically plate-like and closely stacked with a laminated microstructure.