Tuning Αs Precipitation Behavior Via Introducing Sub-Grain Boundaries to Significantly Enhance the Ductility of a High-Strength Metastable Β Titanium Alloy

To overcome the brittleness in high-strength metastable beta titanium alloys, a novel thermomechanical processing route combining hot rolling and dual-step aging was applied to a Ti-4Al-5Mo-5V-5.5Cr-1Nb alloy. By combining hot rolling with a dual-step aging treatment, a high density of sub-grain boundaries and low-angle grain boundaries were introduced, effectively partitioning the prior beta grains. Coupled with the synergistic effects of embryonic omega phase and spinodal decomposition, this approach enabled the uniform precipitation of nanoscale secondary alpha phase (alpha s) both near grain boundaries and within grain interiors. The resulting homogeneous microstructure successfully suppressed strain localization and intergranular fracture. Consequently, the processed alloy achieved an exceptional combination of an ultra-high tensile strength of 1648 MPa and a significantly enhanced ductility of 7.1 % elongation. This work provides a new pathway for designing metastable beta titanium alloys with superior strength-ductility synergy.