Fabrication of γ-TiAl intermetallic alloy using the twin-wire plasma arc additive manufacturing process: Microstructure evolution and mechanical properties

Due to the intrinsic high room temperature brittleness and cold-cracking susceptibility, the fabrication and forming of γ-TiAl intermetallic alloy component is extremely difficult. Therefore, in recent years, a wire-arc additive manufacturing (WAAM) technique has been developed to fabricate the γ-TiAl intermetallic alloy by depositing the Ti and Al wires into a single tungsten arc generated molten pool with specific wire feed ratios. However, the WAAM fabricated γ-TiAl intermetallic alloy has been found having inhomogeneous layer-by-layer microstructure and the excessive heat input of tungsten arc would induce significant residual stress in the bulk sample. In the present paper, the previous WAAM has been further upgraded and an innovative twin-wire plasma arc additive manufacturing (TW-PAAM) process has been developed. Afterwards, a γ-TiAl intermetallic alloy wall component with specific chemical composition of Ti-48Al has been fabricated and the metallography, phase composition and tensile properties are characterized subsequently. It has been found that a significantly more uniform microstructure is obtained in the TW-PAAM fabricated γ-TiAl intermetallic alloy than the previous WAAM technique. The content of α₂ phase, lamellar colony size and lamellar spacing exhibited the tendency of decreasing from the lower to upper part along building direction. And the tensile strength and ductility of the lower section are lower than the middle and top sections. In general, the present TW-PAAM technique has shown promising capability of fabricating γ-TiAl intermetallic alloy with lower cost, and the investigation results would become a valuable reference for understanding the evolution mechanism of microstructure and mechanical properties of the additively manufactured TiAl alloy.