Eliminating layered structure through cyclic heat treatment in SEBM-fabricated TiAl alloy and enhanced tensile properties

Selective electron beam melting (SEBM) enables the fabrication of complex TiAl components but often introduces a macroscopic layered structure due to Al volatilization, leading to microstructural heterogeneity and mechanical anisotropy. To address this, a cyclic heat treatment process is proposed for a SEBM-fabricated Ti-45.5Al-4Nb-1Mo-0.1B alloy. Unlike conventional single-step treatment in the α phase region, the cyclic process involves repeated short-term holding at 1310 °C followed by air cooling. This approach effectively suppresses abnormal α phase growth in Al-depleted regions through the introduction of non-equilibrium γ phase during air cooling, while providing sufficient time for complete γ → α transformation in Al-rich regions. Consequently, a uniform and refined fully lamellar microstructure with an average colony size of ∼32.7 μm is achieved, eliminating the original layered morphology. Tensile tests demonstrate that the cyclically heat-treated alloy exhibits a superior strength-elongation at room temperature, 750 °C, and 800 °C, with notably enhanced elongation up to 15.0 % at 800 °C. The underlying mechanisms of microstructural homogenization and tensile deformation are also elucidated. This work provides a viable post-processing strategy to mitigate microstructural inhomogeneity and in SEBM-fabricated TiAl alloys, paving the way for their high-temperature structural applications.