Effect of substitution of Si by Al on microstructure and synthesis behavior of Ti5Si3 based alloys fabricated by mechanically activated self-propagating high-temperature synthesis

The effect of substitution of Si by Al and mechanical activation on microstructure, phase composition, ignition and combustion temperature of Ti 5 Si 3 based alloys and composites that were prepared by mechanically activated self-propagating high-temperature synthesis (MASHS) method was investigated. For this purpose elemental powders of titanium, silicon and aluminum were mixed according to the 5Ti + 3(1 −  X )Si + 3XAl formula, where X  = 0, 0.2, 0.4, 0.6. The samples were characterized by X-ray diffraction (XRD) analytical technique and scanning electron microscope (SEM) equipped with an energy-dispersive spectrum (EDS) analyzer. The results have shown that formation of Ti 5 Si 3 during milling stage is postponed by adding Al into the system. Presence of Al in the Ti–Si system have a significant effect on the phase composition of the final products. Substitutional solid solution of Ti 5 (Si, Al) 3 and Ti 5 Si 3 –Ti 3 Al composite are formed by increasing Al amount in the system. Furthermore combustion temperature and crystallites size of Ti 5 Si 3 is reduced with addition of Al into the Ti–Si system. Moreover, solubility of Al in Ti 5 Si 3 is increased with enhancing the X up to 0.4, after that, the solubility of Al in Ti 5 Si 3 is ceased, due to achieving the solubility limit of Al in the Ti 5 Si 3 . The average crystallites size of Ti 5 Si 3 are decreased with increasing milling time prior to the reaction.