Enhanced Wear Resistance and Tribocorrosion Performance of New Ti–Zr–Nb–Ta and Ti–Zr–Nb–Mo Alloys for Biomedical Implants

The increasing demand for durable implants, especially for an aging population, has driven the development of new titanium-based alloys with a more desirable combination of properties. This study investigates the effects of alloying titanium with zirconium (Zr), niobium (Nb), tantalum (Ta), and molybdenum (Mo) to enhance its mechanical properties with a focus on wear resistance and tribocorrosion behaviour. A series of Ti-xZr-5Nb-21Ta (x = 20, 30, 40 wt%) and Ti-30Zr-5Nb-xMo (x = 7, 14 wt%) alloys were designed and fabricated via casting. The new alloys were characterised in terms of their microstructure, mechanical properties (including microhardness and Young’s modulus), wear resistance, and tribocorrosion behaviour. The results demonstrated that the alloying elements significantly influenced the microstructure, hardness, and wear resistance. Specifically, the Ti-30Zr-5Nb-14Mo alloy exhibited superior nanohardness (5.32 ± 0.24 GPa) and microhardness (332.25 ± 10.53 HV) than the tested alloys. The Young’s modulus of the alloys ranged from 70.20 ± 2.50 GPa for Ti-30Zr-5Nb-7Mo to 108.26 ± 1.77 GPa for Ti-30Zr-5Nb-14Mo, indicating promising potential for reducing stress shielding. In terms of wear resistance, Ti-30Zr-5Nb-14Mo consistently recorded the lowest volume loss under both dry and PBS conditions across all tested loads. Particularly in phosphate-buffered saline (PBS) solution under higher normal loads, it recorded wear volume losses of 3.24 × 10⁻¹¹ m³ at 17.5 N and 1.09 × 10⁻¹⁰ m³ at 30.8 N, representing reductions of approximately 82% and 57% compared to Ti-6Al-4 V, which exhibited higher volume losses of 1.80 × 10⁻¹⁰ m³ and 2.52 × 10⁻¹⁰ m³ under the same conditions. Under dry conditions, Ti-30Zr-5Nb-14Mo also outperformed all other alloys, including Ti-6Al-4 V, with the smallest wear volume at every load (1.86 × 10⁻¹¹ m³ at 6 N, 9.50 × 10⁻¹¹ m³ at 17.5 N, and 3.18 × 10⁻¹⁰ m³ at 30.8 N). The study highlights the potential of these new titanium alloys as viable alternatives to traditional materials such as Ti-6Al-4 V for biomedical implants and prostheses.