Fracture behavior of micro-sized Ni-P Amorphous alloy specimens has been investigated using a newly developed mechanical testing machine. Specimens with dimensions of 10 × 12 × 50 μm were prepared by focused ion beam machining. Two types of specimens with different crack geometries were prepared. One specimen has a notch with root radius is 0.25 μtm and the other has a fatigue pre-crack. The shapes of the loaddisplacement curves are different for each type of specimen. The fracture strength of the specimens with a notch is higher than that with a fatigue pre-crack and the fracture surfaces of the specimens are also different for each type of specimen. This may be due to the difference in stress concentration at the crack (notch) tip, and indicates that even a notch with a root radius of 0.25 μm is not able to be regarded as a crack for micro-sized specimens. Therefore, the introduction of a fatigue pre-crack is essential for the evaluation of fracture toughness for such micro-sized specimens.

Fatigue life and fatigue crack propagation tests have been performed on microsized Ni-P amorphous alloy specimens to investigate the fatigue properties of this material. The material used was a Ni-11.5 wt%P amorphous thin film. The specimens tested were cantilever-beam-type specimen with dimensions of 30 × 12 × 50 µm 3 prepared by focused ion beam machining. Notches with a depth of 3 µm were introduced in some specimens. The entire set of fatigue tests was performed using a newly developed fatigue testing machine in air at room temperature under a constant load ratio of 0.1. The fatigue life curve was obtained for unnotched specimens, and the fatigue strength of the specimen was determined to be approximately one-third of the static bending strength. Fatigue crack propagation tests were performed using notched specimens. Fine equispaced markings were observed on the fatigue surface. These markings are aligned perpendicular to the crack growth direction, and are considered to be striations. Therefore, even in microsized amorphous alloys the crack is deduced to propagate by cyclic plastic deformation at the crack tip.

Fatigue crack propagation tests at different stress ratios of 0.1 and 0.5 have been performed on microsized Ni-P amorphous alloy specimens to investigate the influence of stress ratio in the crack growth properties of microsized materials. The specimens tested were cantileverbeam-type with dimensions of 10 × 12 × 50 νm3 prepared by focused ion beam machining. Notches with a depth of 3 [m were introduced in all specimens. The entire set of fatigue tests as performed using a newly developed fatigue testing machine in air at room temperature. Fine stripes deduced to be striations were observed on the fatigue fracture surface. Careful measurements of the striation spacings were made. Fatigue crack propagation rate, that is striation spacing, is plotted as a function stress intensity factor range. Fatigue crack propagation rate at stress-ratios of 0.1 and 0.5 in microsized Ni-P amorphous alloy specimens are given by da/dN ∼ 1.3 × 10−8 ΔK;1.16 and da/dN ∼ 3.7 × 10−8 ΔK0.5, respectively. At a given ΔK, crack propagation rate at a stress ratio of 0.5 was higher than that at 0.1. It is considered that a decrease in crack propagation rate at stress ratio of 0.1 is due to adecrease in effective stress intensity factor range ΔKeff, by the effect of crack closure.

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