Peculiar aging response of near β Ti–25 Nb–2Mo–4Sn alloy for biomedical applications

In this paper, aging response of a recently developed near β Ti–25Nb–2Mo–4Sn (wt%) alloy with high strength and low modulus was investigated intensively. The experimental results from X-ray diffraction and transmission electron microscopy showed that the aging production of the Ti-2524 alloy was (β+ω) or (β+α) even under the same aging treatment condition, depending on the pre-treatments prior to the aging. Solid evidence confirmed the competition between stable α phase and metastable ω phase during the decomposition of β phase on aging. Different aging response of Ti-2524 alloy can be attributed to high-density dislocations and grain boundaries which suppress the formation of ω and alternatively promote α phase formation. This provides a thermo-mechanical approach to inhibit deleterious ω phase formation and assist fine α phase precipitation. Upon an appropriate aging treatment, superior mechanical properties of high ultimate tensile strength (1233 MPa) and low elastic modulus (77 GPa) were achieved in Ti-2524 alloy.