真空中および空気中におけるチタニウム材の疲労変形挙動異方性

抄録

To study the fatigue behavior of the cold-rolled titanium plate (KS40) with the texture of the major orientation of (0001) [1010]±30°, the plane bending fatigue tests have been carried out on the specimens (0.3mm thick) cut out parallel (LT) and perpendicular (TL) to the rolling direction, respectively. The tests were conducted in vacuum (1.33×10^-3Pa) and in air at the resonant frequency of about 600Hz for the second-order mode of oscillation. Comparison of the TL with the LT specimens showed that in air the anisotropy was discernible in S-N curves and fatigue crack growth behavior, but hardly in vacuum. In air, the TL specimen had fatigue strength and fatigue crack growth properties greater than the LT specimen and the fracture surfaces appeared more brittle in the TL specimen. It seemed that the character of fatigue behavior in air could be connected with the crystallographic conditions for deformation: the ease of slipping or twinning shear. In vacuum, the specimens raised temperature in themselves up to 45K above room temperature, when cyclically stressed at σ=±201MPa, and fractured in ductile modes. Common microstructure around fatigue cracks was characterized by cell structure both in vacuum and in air, although numerous twins were contained in the specimen prior to fatigue tests. The cells were developed more in vacuum than in air. The results obtained were discussed in connection with the plastic deformability enhanced by internal heating during fatigue testing from the crystallographic points of view.