Effects of thermomechanical history and environment on the fatigue behavior of (β)-Ti-Nb implant alloys

This study examined the fatigue properties of a newly developed cast and thermomechanical processed (beta)-Ti-40Nb alloy for a possible application as biomedical alloy due to exceptional low Young's modulus (64-73 GPa), high corrosion resistance and ductility (20-26%). Focusing on the influence of two micro structural states with fully recrystallized beta-grain structure as well as an aged condition with nanometer-sized omega-precipitates, tension-compression fatigue tests (R=-1) were carried out under lab-air and showed significant differences depending on the omega-phase stability under cyclic loading. Present omega-precipitates stabilized the beta-phase against martensitic alpha '' phase transformations leading to an increased fatigue limit of 288 MPa compared to the recrystallized state (225 MPa), where mechanical polishing and subsequent cyclic loading led to formation of alpha ''-phase due to the metastability of the beta-phase. Additional studied commercially available (beta)-Ti-45Nb alloy revealed slightly higher fatigue strength (300 MPa) and suggest a change in the dominating cyclic deformation mechanisms according to the sensitive dependence on the Nb-content. Further tests in simulated body fluid (SBF) at 37 degrees C showed no decrease in fatigue strength due to the effect of corrosion and prove the excellent corrosion fatigue resistance of this alloy type under given test conditions.