Abstract:

Ti-36Nb-2Ta-3Zr-0.3O (TNTZ-O) is a promising third-generation titanium alloy due to its favorable combination of mechanical properties and biocompatibility. These properties include high strength, a relatively low Young's modulus and the absence of cytotoxic elements. To further assess its suitability for dental implant applications, various heat treatments were performed to investigate the influence of resulting microstructural variations on mechanical and tribological behavior. Samples containing different heat-treated conditions with α (alpha), β (beta), and ω (omega) phases were analyzed and compared with commercially pure titanium Grade 4 and Ti-6Al-4V ELI to evaluate the performance of TNTZ-O relative to established implant materials.

Tribological tests were performed under dry conditions as well as in simulated physiological environments to evaluate friction and wear behavior. Among all investigated conditions, the ω-containing microstructure demonstrates the most stable friction behavior, resulting in the lowest wear volumes. The β-microstructure, comparable to the as-received condition, exhibits pronounced fluctuations in friction behavior with frequent friction peaks, leading to increased wear volumes. This behavior is primarily attributed to the high elastic deformability and adhesive wear characteristics of the β-phase. The presence of α-phase slightly improves friction stability compared to the β-microstructures, as reflected by reduced friction peak intensity. SEM and EDX analyses indicate that adhesive wear and delamination are the dominant wear mechanisms for TNTZ-O, particularly in β- and α-containing microstructures. In contrast, the higher wear resistance of the ω-containing microstructure is attributed to its increased strength and hardness, although its inherent brittleness may limit applicability. By comparison, CP-Ti Grade 4 and Ti-6Al-4V ELI show finer grooves and ridges within the wear tracks, indicative of predominantly abrasive wear.

In addition, cyclic tensile tests were performed on β-TNTZ-O using progressively increasing maximum strain amplitudes and monitored by full-field strain measurements via GOM Aramis. The stress–strain response exhibits a pronounced hysteresis that evolves with cyclic loading, indicating a deviation from linear elastic behavior and a reduction in stiffness at higher strain amplitudes. This response indicates a non-linear deformation behavior of the β phase under cyclic loading, associated with microstructure-dependent and transformation-assisted deformation mechanisms. Compared to the fully β-phase condition, the presence of an α-phase fraction results in a broader and more stable hysteresis response during cyclic loading, suggesting increased energy dissipation due to microstructure-related deformation mechanisms.

Overall, this study demonstrates the strong influence of heat treatments on the mechanical and tribological behavior of TNTZ-O. While the ω-phase offers improved wear resistance, its brittleness limits applicability. The presence of an α-phase provides a promising balance of strength and ductility, whereas the β-phase shows favorable ductility but a pronounced evolution of the stress–strain hysteresis with cyclic loading, associated with a reduction in effective stiffness by progressive strain accumulation. Further optimization through tailored heat treatments and deformation strategies is required to enhance long-term mechanical stability and wear resistance for biomedical applications. The observed cyclic deformation behavior further highlights the need for in situ diffraction-based investigations to directly resolve phase evolution of TNTZ-O during loading.

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Mr. Alexander Rögnitz