The heterogeneity formation mechanism of twin wire-directed energy deposition-arc fabricated TiAl alloy

Additive manufacturing (AM) has become an attractive method in fabricating TiAl alloys. In addition to the well-known anisotropy, additively manufactured TiAl alloys also exhibit heterogeneity. However, research in this area has been limited. This work systematically investigates the heterogeneity formation mechanism of the twin wire-directed energy deposition-arc produced TiAl alloy. The results show that the microstructure characteristics, such as the lamellar spacing (0.39 μm–0.56 μm), colony size (186 μm–232 μm), and α₂ phase content (7 %–10 %), and microstructure degradation degree, present the tendency of increase from the upper to the lower part along the deposition direction, attributed to differences in the thermal cycle features experienced during AM. Consequently, its tensile strength (415.3 MPa–361 MPa) and elongation (0.54 %–0.38 %) also display a gradual decline from the upper to the lower part. This research contributes to a deeper understanding of the evolution of microstructure and the mechanical properties of additively manufactured TiAl alloys.