Formation of MAX solid solutions (Ti,V)2AlC and (Cr,V)2AlC with Al2O3 addition by SHS involving aluminothermic reduction

MAX solid solutions (Ti,V)₂AlC and (Cr,V)₂AlC with Al₂O₃ addition were produced by solid state combustion involving aluminothermic reduction in the mode of self-propagating high-temperature synthesis (SHS). Starting materials included TiO₂/V₂O₅/Al/Al₄C₃ and Cr₂O₃/V₂O₅/Al/Al₄C₃ powder mixtures. Attempts were made to attain (Ti_1−xV_x)₂AlC and (Cr_1−yV_y)₂AlC with the V content in terms of x and y from 0.1 to 0.7. Combustion exothermicity was increased by increasing V₂O₅ for the yield of a higher proportion of V at the substitution site, which not only increased the combustion temperature and reaction front velocity, but also facilitated the evolution of solid solutions. Due to insufficient reaction exothermicity, (Ti_1−xV_x)₂AlC/Al₂O₃ in situ composites were only produced under x≥0.4. On the other hand, the formation of (Cr_1−yV_y)₂AlC/Al₂O₃ was achieved with y from 0.1 to 0.7, because reduction of Cr₂O₃ is more energetic than that of TiO₂. The laminated microstructure characteristic of the MAX ternary carbide was observed for both Al₂O₃-added (Ti,V)₂AlC and (Cr,V)₂AlC composites synthesized in this study.