Significantly enhanced ductility in LPBF-fabricated Ti65 alloy after heat treatment

Additive manufacturing of near-α titanium alloys offers great potential for fabricating complex high-temperature aerospace components; however, the limited ductility of as-built materials remains a key challenge. In this study, a Ti65 alloy was fabricated by laser powder bed fusion (LPBF) and subsequently heat treated at 850 °C, 950 °C, and 1050 °C to investigate the relationships among microstructural evolution, mechanical properties, and deformation behavior. The as-built sample consists entirely of acicular martensitic α′ and exhibits a high tensile strength of 1464.1 MPa but limited ductility of 3.6%. Following heat treatment at 950 °C, the sample exhibits bimodal microstructures composed of primary equiaxed α_p and secondary lath α_s, resulting in an excellent strength–ductility balance with a tensile strength of 1086.2 MPa and an elongation of 20.3%, corresponding to an approximately 464% increase in ductility. The enhanced plastic deformation of the HT-950 sample can be attributed to the cooperative activation of basal, prismatic, and pyramidal <a> slip systems. The combined effects of multi-slip, cross-slip, slip transfer, and minor deformation twinning further mitigate strain localization. The cooperative activation of multiple slip systems enhances deformation compatibility and contributes significantly to the remarkable increase in elongation. These findings provide valuable insights into tailoring the microstructure and optimizing the strength–ductility balance of LPBF-fabricated near-α titanium alloys.