Fatigue performance of low rigidity titanium alloy for biomedical applications

Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged at temperatures between 573 and 723 K after solution treatment at 1063 K have super fine omega phase, or both super fine alpha and omega phases, respectively in beta phase with an average grain diameter of 20 μm. Plain fatigue strength of TNTZ aged after solution treatment is much greater than that of as-solutionized TNTZ in both low cycle fatigue and high cycle fatigue life regions. This is due to the improvement of the balance of strength and ductility by the precipitation of alpha phase. Fretting fatigue strength of TNTZ conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and factional force at the contact plane of pad exist. In fretting fatigue in air, the ratio of fretting damage (P_f/F_f), where P_f and F _f stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer's solution, the passive film on specimen surface is broken by fretting action in TNTZ, which have excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.