Development of Ti-Nb-Mo-Zr Alloys with Low Modulus and Excellent Plasticity for Biomedical Applications

Metastable β titanium alloys with low elastic modulus and excellent plasticity represent highly attractive materials for biomedical stent application. Our work shows that Zr plays a crucial role in regulating β stability to significantly reduce the modulus and enhance plasticity. A series of Ti-25Nb-2Mo-xZr (x = 0, 3, 9, 12 wt%) alloys were designed based on the d-electron theory, and the influence of Zr content on the microstructure, mechanical properties, and deformation mechanism were systematically investigated. The results demonstrated that as the Zr content increases, the β phase stability was significantly enhanced. This leads to, first, the suppressed formation of the high modulus α″ phase and ω phase, which results in the decrease in apparent overall elastic modulus. Second, the dominant mode of deformation shifts from martensite dislocation slip (0Zr) to martensitic variant reorientation (3Zr), then to stress-induced martensite transform (SIMT, 9Zr), and finally to a combination of SIMT and deformation twinning (12Zr). Such shifting effectively increases the alloy's tensile plasticity. Among the series, the Ti-25Nb-2Mo-12Zr alloy exhibited the lowest elastic modulus of 56.3 GPa, together with the highest elongation to failure of 48.2%, demonstrating that the alloy possesses considerable potential for biomedical applications.