Key Takeaways & Executive Findings
- •• Trace oxygen addition effectively stabilizes the β phase in Ti-Nb alloys, reducing elastic modulus from 91 GPa to 24 GPa while maintaining high compressive strength (1404 MPa) and increasing yield strength to 904 MPa. • The low-cost powder metallurgy process enables production of high-performance Ti-Nb alloys for orthopedic implants, offering a cost-effective alternative to expensive manufacturing routes. • Interstitial oxygen modulates thermoelastic martensitic transformation, enhancing shape memory recovery properties, which is beneficial for implant applications requiring recoverable deformation. • The study demonstrates a promising strategy to mitigate stress shielding in orthopedic implants by achieving low modulus comparable to bone (1-18 GPa) without significant strength compromise.
Abstract
Hard tissue repair materials that balance high strength with low modulus are highly promising, representing a transformative focus in applied biomaterials research. In this study, Ti-Nb alloys with high performance are prepared by a low-cost process for orthopedic applications. Phase composition, modulus, compressive strength and recovery properties are effectively manipulated by tailoring trace amounts of interstitial oxygen. With increasing oxygen concentration in sintered Ti-Nb alloys, the β (body centered cubic) phase was stabilized due to the lattice distortion. The elastic modulus declined from 91 to 24 GPa. The compressive strength slightly decreased from 1595 to 1404 MPa and yield strength increased from 760 to 904 MPa. Additionally, the recovery properties were enhanced by the interstitial oxygen as a shape memory alloy. The utilization of trace oxygen serves to modulate the thermoelastic martensitic transformation in Ti-Nb alloys, thereby obtaining appropriate mechanical properties. A notable reduction in modulus is achieved while maintaining high strength, which facilitates the development of orthopedic implants capable of withstanding more complex forces.
1. Introduction
Many metallic materials have recently attracted significant attention for orthopedic applications due to their good biocompatibility and mechanical properties closer to bone [1, 2]. The common metals used in orthopedic biomaterials, especially in replacing shoulders, knees, hips and orodental structures, are 316L stainless steel, Ti and its alloys, Co-Cr, Zr-Ta-Ti [3] and Zr-Nb-Ti-Sn [4] alloys. As the elastic modulus of metals (>100 GPa) is typically much higher than that of bone (1−18 GPa), avoiding the stress shielding effects by modulus matching is an important consideration in the design of orthopedic materials [5, 6]. Porous structures are often introduced to reduce the elastic modulus [2]. Improved fixation can also be achieved by bone tissue growing into and through a porous metal matrix, bonding the implant to the bone host bone [7, 8]. However, not only does this significantly compromise the strength, but there is also the problem of uneven potential distribution due to differences in surface quality, leading to a reduction in corrosion resistance [5, 9−11].
The modulus can also be modulated by phase transformation. NiTi shape memory alloys have a large difference in modulus between martensite (<20 GPa) and austenite (>70 GPa). Different moduli can be obtained by modulating the phase composition. However, Ni ions are potentially harmful to the human body. TiNb alloys are one of most common beta titanium alloys and have excellent biocompatibility widely used in biomedical applications [12−14]. In particular, TiNb also possesses a thermoelastic martensitic transformation [15−18]. The α″ phase (orthorhombic titanium) with higher modulus, and the β phase (body-centered cubic titanium) with lower modulus, together determine the alloy modulus.
Recent studies have shown that the transformation behavior and mechanical properties of TiNb can be effectively adjusted by modulating the interstitial elements [19, 20]. Oxygen has a significant effect on the microstructures and properties of Ti alloys. Lattice expansion due to the oxygen interstitial solid-solution inhibits martensitic transformation and dislocation motion [21]. For Ti-Nb alloys, introducing approximately 1 at% oxygen causes the martensitic transformation temperature (MTT) to decrease by 160 K. This mechanism has been studied extensively. HAMMOND [22] attributed the decrease in the martensitic transformation temperature to the inhibited contraction along the a-axis of the α″ phase (orthorhombic titanium). TAHARA et al [23, 24] and KIM et al [25] found that oxygen stabilizes both the β and α″ phases. Localized nanodomains induced by oxygen atoms in the β phase (body-centered cubic titanium) inhibit the β-to-α″ transformation. The strain-field induced by oxygen promotes the stabilization of the α″ phase. It was reported that oxygen retained the low stability β phase, while reducing the precipitation of α″ and ω (monoclinic structure) martensite [26, 27]. The elastic modulus of Ti-Nb-Ta-Zr-xO decreased as the oxygen content increased. Interstitial oxygen increases the c/a ratio of the β phase, limiting dislocation motion and leadi
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LOU Jia, TANG Xin-dong, DU Chang-hai, LI Dong-yang, LI Yi-min (2026). A low-cost TiNb alloy with high strength for orthopedic implants with low modulus tuned by oxygen concentration. Journal of Central South University. https://doi.org/10.1007/s11771-026-6176-7
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Frequently Asked Questions
What is the main advantage of the TiNb alloy developed in this study?
The TiNb alloy achieves a low elastic modulus (24 GPa) comparable to bone while maintaining high compressive strength (1404 MPa) and increased yield strength (904 MPa), which helps reduce stress shielding in orthopedic implants.
How does oxygen concentration affect the properties of TiNb alloys?
Increasing oxygen concentration stabilizes the β phase, reduces the elastic modulus from 91 to 24 GPa, slightly decreases compressive strength, increases yield strength, and enhances shape memory recovery properties by modulating the thermoelastic martensitic transformation.
What is the significance of using a low-cost process for TiNb alloy production?
The low-cost powder metallurgy process makes the production of high-performance TiNb alloys more economical, potentially increasing their accessibility for orthopedic implant applications.
Why is low modulus important for orthopedic implants?
Low modulus helps avoid stress shielding, a phenomenon where the implant bears most of the load, leading to bone resorption and implant loosening. Matching the modulus of bone (1-18 GPa) promotes better load sharing and implant longevity.
What are the potential applications of this TiNb alloy?
The alloy is intended for orthopedic implants such as bone replacement and fixation devices, where a combination of high strength, low modulus, and good biocompatibility is required.
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