Abstract: β titanium alloys show great potential in biomedical implant applications for excellent biocompatibility and low elastic modulus. However, current research on the superelasticity of β titanium wire is limited, and the achieved performance is still suboptimal. Here we developed a Ti-24Nb-4Zr-8Sn wire with enhanced superelasticity and fatigue reliability via cold drawing and one-step flash heat treatment at 923 K for 7 min. The tailored dual-phase heterostructure is characterized by equiaxed β grains and α″ laths inherited from the as-drawn state. The α″ laths are distributed along grain boundaries and parallel to the wire axis. Such a heterostructure reduces phase transformation energy, enables the stress-induced martensitic transformation to preferentially occur through the migration of the β/α″ phase boundary, and provides abundant nucleation sites for martensite growth, while cyclic loading induces a favorable <110>_β texture for martensitic transformation. As a result, the wire yields a high recoverable strain (3.6 %) and an exceptional fatigue life exceeding 20,000 cycles under 450 MPa loading. This work presents a microstructural design strategy for the development of high-performance biomedical wires.

Key words: β titanium wire, Phase heterogeneity, Martensitic transformation, Shape memory alloy, Superelasticity