A metastable β Ti alloy was additively manufactured by laser powder bed fusion (LPBF). Tensile testing along the build direction of the as-LPBF material (LPBF-0°) revealed significant work softening immediately following yielding with no uniform deformation. By contrast, substantial work hardening and uniform elongation well over 10% were achieved perpendicular to the build direction (LPBF-90°). Similar effects were obtained in the build direction after super transus heat treatment (LPBF-0°+HT) although the strength was slightly lowered. In addition, the yield drop phenomenon observed in both orientations of the as-LPBF materials disappeared after HT. The enhanced work hardening ability, and thus ductility, can be attributed to increased interactions of slip bands/slip bands owing to additional {112}<111> slip systems becoming operative in LPBF-0°+HT and LPBF-90° while LPBF-0° was dominated by {110}<111> only. The other variations after HT may be related to the coarsening of grain structure and removal of specific substructures in the as-LPBF microstructure.

A ternary hybrid Ti alloy (HYTA) was produced by selective laser melting (SLM), combining all three classes of the titanium system. The hybridisation of the α CP Ti, α-β Ti-64 and β Ti-5553 gave rise to a highly heterogeneous microstructure encompassing all the possible phases and structures which do not co-exist in conventional monolithic Ti alloys. The details of the complex microstructure were comprehensively characterised, revealing the roles played by such important factors as the distribution of the ingredient alloy particles, the Marangoni convection and diffusion of solute during melting, and microsegregation of solute during solidification. The ternary HYTA exhibited an excellent combination of high tensile yield strength of 1000 MPa and enhanced ductility with uniform elongation of ∼15% and total elongation of ∼20%, superior to conventional Ti alloys of various types. Such exceptional performance is attributed to the high-degree heterogeneity and the operation of most major deformation mechanisms which coordinate effectively and transfer smoothly between various parts with a wide range of hardness (4–6 GPa). The outcome has further demonstrated the potential of hybridisation of microstructures as a new strategy for future alloy development.