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Ti-6.5Al-2Zr-1Mo-1V (TA15), widely used in the aerospace industry, is a medium- to high-strength, near-α titanium alloy with high aluminium equivalent value. The TA15 fabricated via laser powder bed fusion (L-PBF) normally presents a typical brittle appearance in as-built status, with high strength and low ductility. In this study, the microstructure and properties of L-PBF TA15 were engineered by various heat treatments below the β-transus temperature (1022 °C). After heat treatment, the original acicular martensite gradually transforms into a typical lamellar α + β dual-phase structure. Withannealing temperature increases, the lamellar α phase thickened with a decreased aspect ratio. Globularisation of the α grain can be noticed when annealing above 800 °C, which leads to a balance between strength and ductility. After heat treatment between 800–900 °C, the desired combination of strength and ductility can be achieved, with elongation of about 12.5% and ultimate tensile strength of about 1100 Mpa. [ABSTRACT FROM AUTHOR]

A better combination of strength and plasticity may be imparted by the tri-modal microstructure in titanium alloys than the as-built acicular martensite. It is generally conceived that hot working is required for the globularization of the α phase in traditional manufacturing. In this article, we report an innovative strategy to obtain a tri-modal microstructure consisting of globularized α in laser powder bed fusion (L-PBF) Ti–6.5Al–2Zr–1Mo–1V (TA15) alloy, which only consists of post-process heat treatment. A tri-modal microstructure formed by the equiaxed α, lamellar α, and transformed β matrix may be effectively introduced by the multiple annealing heat treatment. A significant improvement in ductility by 72.32% was obtained with final microstructure leads, maintaining a desired high strength and providing tensile properties comparable to those of its forging counterparts. [Display omitted] • The triple heat treatment parameters in the field of L-PBF Ti alloy are studied. • An ideal tri-modal microstructure consisting of ~17% equiaxed α, ~48% lamellar α and ~35% transformed β matrix is obtained. • The optimal tri-modal microstructure is an effective and practical microstructure for the balance of plasticity and strength of titanium alloys. • The globularization of the primary α satisfies the boundary-splitting globularization mechanism. [ABSTRACT FROM AUTHOR]