Precipitation-assisted microstructural stabilization and twin-mediated strength-ductility synergy in EB-PBF TiAl alloys

Abstract

Inherent microstructural inhomogeneity and limited ductility remain major obstacles to achieving superior strength-ductility synergy in additively manufactured TiAl alloys. In this study, a TiAl-Si alloy was fabricated by electron beam powder bed fusion and tailored through a two-step heat treatment to control its microstructure and mechanical performance. The resulting alloy exhibits a hierarchical multiscale architecture. Atom probe tomography reveals that nanoscale Ti5Si3 precipitates partially dissolve while submicron particles are retained, stabilizing the lamellar structure through Zener pinning and diffusion inhibition, and effectively suppressing coarsening. Transmission electron microscope observations further identify three twin-twin interaction modes that activate defect-mediated mechanisms triggered by local stress concentrations, thereby accommodating strain and sustaining plastic flow. Consequently, the alloy achieves an ultimate tensile strength of ∼1050 MPa and significantly enhanced elongation relative to the as-built state. This strength-ductility synergy arises from the decoupled yet complementary effects of precipitate-stabilized lamellae and twin-interaction-induced plasticity, establishing a mechanistic framework for designing additively manufactured TiAl alloys.