In-situ modulation mechanisms of TiAl alloys fabricated by electron beam powder bed fusion on microstructure and mechanical properties

Abstract

This study elucidated the microstructure-tensile property evolution of TiAl alloys through synergistic modulation of scanning speed and beam current. As scanning speed and beam current increased, coarse γ bond-like phases transited into refined α₂/γ lamellar colonies with preferential 0°/45° orientations relative to the building direction, accompanied by increased phase fractions of α₂ (0.194 % → 0.388 %) and B2 (0 % → 0.87 %). Meanwhile, at room temperature, the tensile strength increased to ∼650 MPa due to the enhanced refinement of lamellar colonies, while the elongation decreased owing to the presence of brittle B2 phase, with the fracture mode characterized by quasi-cleavage fracture. At 700 °C, the facture elongation rose, owing to the high toughness of B2 phase and the increased activity of slip-twinning in TiAl alloys. The tensile strength remained similar to that at room temperature, with the fracture mode being predominantly intergranular. Furthermore, the specimen with γ bond-like phases exhibited significant differences in elongation between the directions parallel and perpendicular to the building direction, demonstrating anisotropy. These findings establish an integrated process-microstructure-property optimization strategy for designing advanced TiAl alloys in aerospace directional-load components, particularly addressing performance requirements under complex thermo-mechanical environments.