Enhanced strength and work hardening in Ti–10V–2Cu–3Al alloy associated with liquid-nitrogen-quenching-induced changes in internal twinning behavior of orthorhombic α″ martensite

: The use of orthorhombic martensite (α″) in Ti alloys has attracted attention because of its relatively low Young’s modulus, but it remains insufficiently explored as a basis for microstructural strengthening. Enhancing its strength and work hardening while retaining the low modulus would make α″-based Ti alloys promising for biomedical and lightweight structural applications. Here, we propose liquid nitrogen quenching (LNQ) as a strategy for controlling the cooling rate to tailor hierarchical α″ martensitic microstructures and deformation-twinning behavior in single-α″ Ti–10V–2Cu–3Al. Compared with water quenching (WQ), LNQ refined α″ martensite plates and increased the density of the internal twins introduced for accommodating the transformation strain. Microstructural analyses show that faster cooling suppressed the thickening of the internal twins and shifted the dominant accommodation mode from twin growth to twin nucleation. This cooling-condition-dependent internal state also altered the tensile deformation: the WQ sample accommodated plastic strain mainly through growing the existing deformation twins, whereas the LNQ sample preferentially introduced additional twins with different orientations. Consequently, LNQ increased the apparent critical stress for macroscopic deformation twinning from 473 ± 27 to 601 ± 36 MPa and the ultimate tensile strength from 712 ± 12 to 845 ± 37 MPa, while maintaining a low Young’s modulus of 82.5 ± 1.6 GPa and plastic elongation of 19.7 ± 1.6%. These findings demonstrate that cooling-rate-induced hierarchical twinning control effectively enhances the strength and work hardening while preserving the low-modulus advantage of α″-based Ti alloys.