Hf-induced solute drag regulates silicide precipitation for enhanced thermomechanical performance in near α-Ti alloys

To address the severe reduction in elongation of near‑α titanium alloys caused by the formation of continuous, brittle silicides during long‑term high‑temperature aging, this study exploits the low diffusivity of Hf to investigate its influence on phase formation during prolonged aging and to elucidate the synergistic mechanism responsible for balancing strength, ductility, and thermal stability. Hf forms a substitutional solid solution with Ti, introducing pronounced local lattice distortion and elastic strain fields; this markedly increases the diffusion activation energy and migration barrier of Si atoms, thereby blocking their directed long‑range diffusion toward phase boundaries. Consequently, the kinetic conditions required for the continuous growth of brittle interfacial silicides are fundamentally suppressed. In addition, the Hf‑induced solute‑drag effect, together with a reduction in the α/β lattice misfit from 2.32% to 1.84%, effectively inhibits the preferential growth of coarse α colonies and promotes the nucleation of secondary phases. After aging at 650 °C for 100 h, silicide precipitates transformed from a 111.4 nm continuous interfacial film to fine, uniformly dispersed intragranular/interfacial nanoparticles with an average size of 61.6 nm; accordingly, the Ti‑5.0Hf alloy achieves an excellent room‑temperature strength–ductility synergy (1143 MPa tensile strength and 8.3% elongation), exhibits outstanding softening resistance over 600–750 °C (536 MPa at 750 °C), and retains 54.2% of its initial ductility after long‑term aging. This work establishes a quantitative structure–property relationship between lattice effects induced by low‑diffusivity solutes and silicide kinetics, providing design guidance for high‑temperature structural alloys that balance thermal strength and aging stability.