2009 年 50 巻 7 号 p. 1713-1719
Fatigue behaviors of ultra fine wires of β-type Ti-14Mo-3Nb-1.5Zr alloy and α-type Ti-10Zr alloy and α-type CP (commercially pure) titanium with diameters in the range of 35–100 μm were investigated by rotating-bending fatigue testing in 1 mass% lactic acid solution maintained at 310 K. The maximum number of cycles during fatigue testing was 107. The β-type Ti-14Mo-3Nb-1.5Zr alloy wires showed a clear fatigue limit. On the other hand, the α-type Ti-10Zr alloy wire and α-type CP titanium wire did not show a clear fatigue limit, and their fatigue strengths gradually decreased with decreasing maximum bending stress. The fatigue limit of a β-type Ti-14Mo-3Nb-1.5Zr alloy wire with a polished surface was greater than 50% of its tensile strength, while the fatigue limits of titanium wires with as-drawn surfaces were less than 50% of their tensile strengths. Surface defects that were introduced during the cold drawing process of the wires might act as crack origins of the fatigue fracture. Therefore, surface polishing is an effective technique for improving fatigue properties of titanium wires. The elution of metallic ions from the wires into the 1 mass% lactic acid solution was suppressed at a very low level during fatigue testing of all the investigated titanium wires.
