Directional orthorhombic phase precipitation and coarsening enable strength-ductility synergy in compositionally modified Ti 2 AlNb-based alloys

Ti2AlNb-based intermetallic alloys are promising candidates for aero-engine hot-end components, yet their intrinsic covalent bonding inevitably causes a strength-ductility trade-off that limits their engineering applications. Herein, a novel strategy integrating directional O-phase precipitation and coarsening is proposed to achieve excellent strength-ductility synergy in newly designed Ti2AlNb-based alloys. Four alloys with reduced Al and Nb contents were designed, three of which were further modified with Zr and Mo. Among them, the as-cast Ti-20Al-21Nb-2Zr-0.5Mo (A2) alloy exhibited the most favorable tensile performance. Severe cold rolling coupled with short-term direct aging at 880 °C induces the directional precipitation of dense and fine lamellar O-phase. Dislocations and banded substructures provide abundant heterogeneous nucleation sites, while local stress fields and B2/β texture constrain lamellar growth to form a well-aligned microstructure. Prolonged aging primarily enlarges interlamellar spacing, accompanied by a slight decrease in the O-phase area fraction, whereas elevated aging temperatures lead to O-phase coarsening and partial dissolution. These unique microstructural evolutions effectively break the inherent performance bottleneck. The cold-rolled A2 alloy aged at 880 °C for 30 min exhibits superior comprehensive properties, with a room-temperature yield strength of 1,046 MPa, tensile strength of 1,223 MPa, elongation of 9.6%, and a high-temperature tensile strength of 943 MPa at 650 °C, outperforming most previously reported Ti2AlNb alloys. The coordinated deformation mechanisms stem from concentrated dislocations in B2/β channels and interfacial dislocation pile-ups ensuring high strength, while continuous B2/β channels accommodate plastic strain. This work provides a feasible guideline for composition optimization and short-process manufacturing of high-performance Ti2AlNb alloys.