Strengthening Near-α Titanium Alloys via Phase-Transformation-Induced High-Density Nanotwins

To address the challenge of inducing high-density twin substructures via phase transformation in near-α titanium alloys, which is restricted by the high stacking fault energy of the hexagonal close-packed structure, this study aims to achieve the controllable formation of high-density nanotwins by exploiting the structural transformation characteristics of the martensitic transformation. The results indicate that as the solution temperature increases, the microstructure evolves from a basket-weave α + β dual-phase structure to fine acicular α′ martensite. Notably, high-density nanotwins were induced within the α′ laths after water quenching from 1090°C. This microstructural evolution is attributed to the severe lattice shear and high strain-energy accumulation during the martensitic transformation, where the substantial transformation strain energy is accommodated by a self-coordinating shear mechanism through the formation of twins. Mechanical testing reveals that the tensile strength initially increases and then decreases with solution temperature. The 1090°C-treated alloy exhibits a peak room-temperature ultimate tensile strength (UTS) of 1425.9 MPa with an elongation of 6.6%, while retaining a high UTS of 1005.2 MPa and an elongation of 8.8% at 600°C. The high-density nanotwin boundaries constitute a dense network of barriers to dislocation motion, providing a significant contribution in static strengthening at both room and elevated temperatures.