The mechanical behavior of TiNbSn alloys according to alloying contents, cold rolling and aging

Structure and Properties of Metastable β Ti-25Nb-8Sn Alloy following Cold Rolling and Aging Treatments

Metal implants require an elastic modulus close to cortical bone (<30 GPa) to avoid stress shielding and ensure adequate load-bearing strength. The metastable β-type Ti-25Nb-8Sn alloy has a low elastic modulus (52 GPa), but its yield strength (<500 MPa) needs enhancement. This study enhances Ti-25Nb-8Sn's elastic admissible strain through cold rolling and aging heat treatments, investigating the microstructure's impact on mechanical and corrosion properties. The results show that lower-temperature aging (<450 °C) leads to ω-phase precipitation, yielding a 300% increase in yield strength (>1900 MPa). However, this also increases the elastic modulus (~80 GPa), limiting the deformation ability. Higher-temperature aging (>500 °C) eliminates the ω phase, transforming it into α precipitates, resulting in a lower elastic modulus (~65 GPa) and improved deformation ability, with substantial yield strength (>1000 MPa). In summary, the optimal process conditions are determined as 90% cold rolling followed by aging treatment at 550 °C. Under these conditions, Ti-25Nb-8Sn achieves the most suitable yield strength (1207 MPa) and high corrosion resistance, retaining a relatively low elastic modulus (64.7 GPa) and high elastic admissible strain (1.93%). This positions it as an ideal material for biomedical implants.

Origin of low Young modulus of multicomponent, biomedical Ti alloys - Seeking optimal elastic properties through a first principles investigation

Multicomponent, biomedical β-Ti alloys offer ultra-low Young modulus values that are related to a unique and poorly understood reduction of C₄₄ and C' elastic constants in comparison with binary systems. The elastic properties of such materials are difficult to control due to the large variations occurring even for a small change in chemical composition, which cannot be explained using existing theories. In this article, we investigate the above issues through systematic ab initio elastic constants calculations for a series of binary, ternary and quaternary Ti alloys. Special attention is paid to examining the reliability of the methodology adopted and to clarifying the atomic scale mechanisms that affect the mechanical properties of the systems analysed. It was found that the lower boundary of the polycrystalline Young modulus of Ti-Nb-base β phase is close to 50 GPa, and strongly depends on two specific electronic hybridisations related to niobium and simple metals addition that control C₄₄ and C'. Based on the relationship established between electronic structure and mechanical properties, we propose several quaternary alloys whose directional <100> Young modulus values are equal or similar to that of human bones. Some electronic-based guidelines for designing new multicomponent β-Ti alloys are also formulated.