The Effect of Al Loss on the Microstructural Formation of TiAl Alloys Produced via Direct Laser Deposition

Additive manufacturing is becoming a popular and effective process for lightweight high-temperature TiAl alloys, but there is a lack of understanding regarding the corresponding microstructural formation mechanisms. In this study, various Ti-47Al-2Cr-2Nb alloys were additively manufactured with different laser power values, and the related microstructures were carefully characterized. The results show that a convoluted microstructure, a nearly full α2/γ lamellar structure, and an α2/β Widmanstatten structure were obtained as the laser power was increased. Moreover, the Al content of the as-deposited specimen decreased from 47 at.% to 40 at.%, which is considered to have strongly affected microstructural formation. As the Al content decreased, the solidified microstructure transformed from hexagonal dendritic α2 to orthogonal dendritic β and cellular β, successively. Moreover, massive α → γ transformation is more likely when the Al content is high, and α → α2 transformation tends to occur when the Al content decreases. The microstructure evolution processes are evaluated in the present paper by synthesizing the experimental results with a thermodynamics analysis.