Strength–Ductility Enhancement in Additively Manufactured Titanium Alloys via Neutral Element‐Mediated Microstructural Control

To overcome the challenges of the strength‐ductility trade‐off in laser additively manufactured (LAM) titanium alloys, and to avoid the intragranular microstructure degradation often caused by an exclusive focus on grain equiaxialization, this work proposes a novel strategy of “grain morphology‐intragranular microstructure co‐optimization” guided by the addition of the neutral element Zr. Two alloys with distinct Zr contents, Ti‐6Al‐4V‐2Cr‐1Mo‐ x Zr (Ti‐6421‐ x Zr; x = 3, 25), were developed and prepared by laser direct energy deposition (DED). The results demonstrate that Zr not only enhances the columnar‐to‐equiaxed transition (CET) capability and induces lattice expansion to achieve fully equiaxed fine grains, but also exhibits β‐like stabilizing effects that refine and homogenize the intragranular α‐laths, thereby enhancing the overall mechanical performance. Compared with the Zr‐free DED Ti‐6Al‐4V‐2Cr‐1Mo (Ti‐6421) alloy, the Ti‐6421‐3Zr alloy exhibits a ∼15% increase in yield strength (∼1025 MPa) while maintaining a comparable excellent elongation (∼15.7%), whereas the Ti‐6421‐25Zr alloy exhibits an ultrahigh tensile strength exceeding 1300 MPa (ultra‐high strength), coupled with a substantial ∼42% enhancement in yield strength (∼1258 MPa), while maintaining a considerable ductility of ∼10.5%, demonstrating excellent strength‐ductility matching in both cases. This work highlights the distinctive role of neutral Zr in enabling microstructural synergy and strength‐ductility integration, offering a promising pathway for high‐performance LAM titanium alloys.