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 Ti₅Si₃ 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 Ti₅Si₃ 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 Ti₅(Si, Al)₃ and Ti₅Si₃–Ti₃Al composite are formed by increasing Al amount in the system. Furthermore combustion temperature and crystallites size of Ti₅Si₃ is reduced with addition of Al into the Ti–Si system. Moreover, solubility of Al in Ti₅Si₃ is increased with enhancing the X up to 0.4, after that, the solubility of Al in Ti₅Si₃ is ceased, due to achieving the solubility limit of Al in the Ti₅Si₃. The average crystallites size of Ti₅Si₃ are decreased with increasing milling time prior to the reaction.