Abstract: Titanium aluminide (TiAl) alloys, known for their light weight and high specific strength, hold promising potential for aerospace applications. Recent studies have focused on improving their properties through composite strengthening. An in situ synthesized Ti₅Si₃- reinforced TiAl composite with excellent performance was successfully fabricated via a dual-wire electron beam-directed energy deposition (EB-DED) process. The microstructure of the as-deposited Ti₅Si₃/TiAl composite consisted of primary Ti₅Si₃ rods, eutectic Ti₅Si₃ needles, and lamellar TiAl+Ti₃Al structures. The phase transformation during the EB-DED process was L→Ti₅Si₃+L→Ti₅Si₃+(α+Ti₅Si₃)_Eutectic→Ti₅Si₃+(Ti₃Al+TiAl)_Eutectoid. The expanded Blackburn orientation relationships among the ternary phases emerged from the eutectic reaction of L→α+Ti₅Si₃ with an undercooling exceeding 136 °C and the subsequent eutectoid reaction with ordering transformation and were expressed as $<11 \overline{2} 0>_{\mathrm{Ti}_{3} \mathrm{Al}}$//$<10 \overline{1} 0>_{\mathrm{Ti}_{5} \mathrm{Si}_{3}} $//$<1 \overline{1} 0>_{\mathrm{TiAl}} \text { and }\{0001\}_{\mathrm{Ti}_{3} \mathrm{Al}} / /\{0001\}_{\mathrm{Ti}_{5} \mathrm{Si}_{3}} / /\{111\}_{\mathrm{TiAl}}$. The Ti₅Si₃ phase had a greater hardness than did the lamellar structures and enhanced the mechanical properties of the matrix. The compressive yield strengths at room temperature and 750 °C were 1221±51 and 1034±34 MPa, respectively, whereas the tensile yield strength was 347.4±12.7 MPa at 950 °C, surpassing those of other TiAl alloys. The calculated strength with different strengthening mechanisms was 1056.4 MPa, and the greatest improvement in strength was attributed to the decreased interlamellar spacing. This work provides critical insight into the design of TiAl composites with superior mechanical properties and aids in understanding the microstructural evolution of as-deposited Ti₅Si₃/TiAl composites.

Key words: Ti₅Si₃/TiAl composite, Electron beam-directed energy deposition, Microstructure evolution, Orientation relationship, Mechanical property