Evaluation of the crystal rotation behavior at the fatigue crack tip in pure titanium films

Using a fatigue testing method by which fatigue cracks can be initiated and propagated in a film adhered to cover an elliptical through-hole in a base plate subjected to push-pull cyclic loads, annealed pure titanium films with the thickness of 90 μm were fatigued under a constant stress amplitude with a stress ratio of -1. The crystal rotation behavior with the tensile/compressive loading at the fatigue crack tip was evaluated from the crystal orientation measured by EBSD (Electron Back-scatter Diffraction) method. The titanium films under the tensile/compressive stress condition were prepared as follows; the films were adhered to the base plates loaded by a servo hydraulic testing machine, then the base plates were detached from the testing machine. From the crystal rotation behavior at the fatigue crack tip, it was found that the crystal rotation angle was relatively small and the rotation axis tended to different directions between the upper side and lower side of the grain in front of the crack tip. The fatigue crack propagated along the borderline between two regions in the crystal grain where the crystal rotation axes with different directions were obtained before the fatigue crack propagation. (author)