respectively. However, these values are not valid plane strain fracture toughness values (KIC), as the criteria of plane strain requirements were not satisfied for this specimen size. Actually, a plastic zone was observed clearly at the crack tip. As the plane strain requirements are determined by K and σy (yield stress), it is rather difficult for micro-sized specimens to satisfy these requirements. Consequently, another criterion such as J integral might be required to evaluate fracture toughness of such micro-sized specimens. Fracture Surfaces Figures 4 (a) and (b) show scanning electron micrographs of fracture surfaces for the specimens with different crack orientations. Fine equispaced markings aligned perpendicular to the crack propagation direction are observed ahead of the notch. This kind of markings were also observed on fatigue fracture surface of micro-sized Ni-P amorphous alloy specimens in our previous investigation [7], and are considered to be striations. Vein patterns which have been observed on static fractured surfaces on Ni-P amorphous alloy are visible ahead of the fatigue pre-cracked region. The fracture surface of the in-plane type specimen is relatively flat. In contrast, the fracture surface of the out-of-plane type specimen is rough, and the crack seems to propagate tortuously. The difference in KQ values is considered to result from the difference in fracture surface morphologies. (a) 5µm Notch (b) Notch Figure 4: Scanning electron micrographs of fracture surfaces of (a) in-plane type specimen and (b) out-of-plane type specimen, respectively. Another notable feature of the fracture surface is the existence of slant fractured regions near the side surfaces of the crack. The width of the slant fractured region is approximately 1 µm for in-plane type specimens and 3 µm for out-of-plane type specimens. If these are shear lips, these regions should be plane stress dominated regions. The expected width of the shear lip is then calculated based on fracture mechanics [8]. The calculated value of shear lip width at KQ is 1.2 µm for in-plane type specimen and is 3.4 µm for out-of-plane type specimen (the value of σy = 2.0 GPa in this amorphous alloy thin film was quoted in this calculation [9]). These sizes are very close to those of the slant fractured regions in Figs. 3 (a) and (b). Therefore, these slant fractured zones are considered to be plane stress dominated regions and the flat region is considered to correspond to plane strain dominated one. Origin of Anisotropic Fracture The provisional fracture toughness, KQ, of the out-of plane specimen was much higher than that of the in-plane specimen. Electron diffraction pattern of the Ni-P amorphous alloy thin film (the beam direction is parallel to the deposition growth direction) showed only a halo pattern which is characteristic of an amorphous phase. Therefore, there is no medium or long range ordering in the direction perpendicular to the deposition growth direction in this amorphous thin film. However, it has not been confirmed whether there is medium or long range ordering in the direction parallel to the deposition
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