The Ti-6Al-4V alloy is widely used in orthopedic implants due to its favorable mechanical properties and biocompatibility. However, its significantly higher elastic modulus relative to human cortical bone to stress shielding, which can result in secondary fractures. To address this issue, low-modulus Ta-Ti alloys have been developed for biomedical applications. Despite their promise, the fatigue behavior of these alloys remains insufficiently characterized. This study investigates the fatigue performance of Ta-Ti alloys subjected to four distinct heat treatment conditions: ST890-Ag500 and ST700-Ag500 (solution-treated at 890 °C and 700 °C, respectively, followed by aging at 500 °C), ST750 (solution-treated at 750 °C), and Ag500 (aged at 500 °C without prior solution treatment). For each condition, two types of specimens-smooth and circumferentially notched- were fabricated and tested using plane bending fatigue experiments. The results revealed that circumferentially notched specimens exhibited a fatigue limit of approximately 180 MPa, while smooth specimens demonstrated higher fatigue limits ranging from 200 to 270 MPa. Across all heat treatment conditions, the Ti-6Al-4V alloy consistently exhibited superior fatigue strength at 10⁷ cycles compared to the Ta-Ti alloys, regardless of the presence of notches. Furthermore, in notched Ta-Ti specimens, fatigue cracks initiated at stress concentration sites under cyclic loading, and fatigue life could be reasonably interpreted based on these observations. These finding suggests that the presence of a notch mitigates the influence of heat treatment parameters-such as grain size, microstructural features, and elastic modulus- on fatigue performance, relative to the impact on smooth specimens.
HATTA et al. (Wed,) studied this question.