Combustion synthesis of (Ti1−xNbx)2AlC solid solutions from elemental and Nb2O5/Al4C3-containing powder compacts

Preparation of the (Ti1−xNbx)2AlC solid solution (formed from the Mn+1AXn or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2–0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)2AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti1−xNbx)2AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb2O5, and Al4C3 were adopted for the in situ formation of Al2O3-added (Ti,Nb)2AlC. The SHS process of the Nb2O5/Al4C3-containing sample involved aluminothermic reduction of Nb2O5, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)2AlC. Based upon the XRD analysis, two intermediates, TiC and Nb2Al, were detected in the (Ti,Nb)2AlC/Al2O3 composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al2O3-added (Ti,Nb)2AlC solid solutions synthesized in this study.