Microstructural adjustments and mechanical properties of a cold-rolled biomedical near β-Ti alloy sheet

In this study, microstructural adjustments and mechanical properties of a cold-rolled nearβ-type alloy Ti-25Nb-3Zr-3Mo-2Sn (wt%) sheet were investigated.Microstructures and phase transformation products strongly depended on aging temperatures. Solution treatments within singleβ-phase field removed the stress-inducedα″martensites and produced a few new lath-shaped ones, but metastableβphase still dominated. This is exactly the reason why current alloy exhibits the lowest modulus (54 GPa) and best elongation to fracture (39%),but the worst yield strength of only 340 MPa, at solutiontreated state. A fairly large number of ellipsoidalωphase nanoparticles precipitated throughout parentβphase during aging at 380℃. Theseωnanoparticles possess remarkable strengthening effect, but deteriorate ductility seriously. A novel post-aging process was proposed to remove brittleωphase. By contrast, aging at 450℃resulted in sufficient precipitation of fine needle-like a phase. This brought about the best combination of high yield strength (770 MPa) and moderate elastic modulus(75 GPa) and good elongation (15%) for biomedical implants.