Enhancing strength and ductility in high Nb-containing TiAl alloy additively manufactured via directed energy deposition

Intermetallic TiAl alloys have found applications in the aerospace and automotive fields. Nevertheless, to satisfy the increasingly complex environmental requirements, these lightweight alloys must be improved particularly in strength and ductility. Additive manufacturing (AM) exhibits a rapid solidification rate and may strengthen intermetallic TiAl alloys. In this study, an additively manufactured (AMed) Ti-48Al-8Nb alloy with fine formability was successfully fabricated by optimizing the power used during directed energy deposition. The preferential crystal plane for the obtained alloy is {111}γ due to its lowest surface energy, and the presence of the thermal gradient during the AM process results in the alloy growing along the building direction. The TiAl alloy AMed at 500W delivers an excellent tensile strength of 880MPa that is 1.71 times higher than that of its as-cast counterpart, as well as elongation of 0.7% at room temperature. The superior properties of this alloy are due to the formation of numerous deformation twins during tensile deformation at room temperature that enables twin intersections to produce high-density nano-twins while contributing to stress release. Moreover, the AMed TiAl alloy exhibits outstanding high-temperature strength retention performance.