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

• Ti5Si3–Ti3Al nanocomposite were synthesized by MASHS method.
• Ti5Si3 Crystallites size was decreased by increasing pre-milling time prior reaction.
• Combustion temperature was decreased with increasing of Al content in system.
• Solubility of Al in Ti5Si3 was increased by enhancing Al in system.
• Al prevented formation of any product in Ti–Si–Al system during milling even after 6 h.

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.

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