Achieving stable ultra-low elastic modulus in near-β titanium alloys through cold rolling and pre-strain

Achieving ultra-low modulus in titanium alloys to address the stress shielding effect has been a longstanding challenge. In recent years, increasing the martensite/austenite interfaces as much as possible has emerged as a novel approach to reducing the elastic modulus of titanium. Research on Ti2448 demonstrated that inducing martensitic transformation through pre-strain to increase the interfaces can indeed achieve extremely low elastic modulus values (<20 GPa); however, due to the low martensitic transformation temperature, this modulus only persists for 6 days at room temperature before reverting, which is unacceptable for long-term applications in the human body. In this study, minor cold rolling (25 % thickness reduction) and pre-strain (1.5 % tensile strain) were applied to a near-β titanium alloy Ti-26Nb-4Zr-4Sn-1Mo-1Ta (wt %) with nanoscale martensite distribution. An ultra-low elastic modulus of 31.5 GPa and moderate strength of 590 MPa were achieved in this alloy. The formation of finer and more dispersed nano martensitic domains due to cold rolling, along with further martensitic transformation induced by pre-strain, maximizes the martensite/austenite interface, and results in such ultra-low elastic modulus. The elastic modulus obtained through this method can be maintained for over one year at room temperature. Further characterization revealed that the formation of nanoscale martensite in this alloy is driven by a combination of compositional factors, internal stresses induced by rapid quenching (182.9 ± 48.4 MPa), and the inhibitory effect of the ω phase. This simple and feasible interface engineering method broadens the compositional design space for low modulus titanium alloys, providing new insights for future research on biomedical titanium alloys.