Statistical Fatigue Property of Multi-Layer Amorphous Metal Composites in Axial Loading

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Statistical fatigue property and fracture mechanism of a Fe-based film amorphous metal, Fe78B13Si9, have been examined in the axial loading. Testing specimens including single-layer and multi-layer types were prepared from a long ribbon of Fe78B13Si9 amorphous metal with dimensions of 25µm in thickness and 50mm in width. The high cycle fatigue tests were performed by using electro-hydraulic servo testing machine in tension-tension loading at a frequency of 50 Hz with the stress ratio of 0.1. The testing data showed that fatigue lives of the amorphous metal had a large scatter, especially at low stress levels. By applying common Weibull distribution and mixed-mode Weibull distribution, the statistic fatigue property of the specimens was quantitatively analyzed. The fatigue strength σ at N=107 was in the range of 135-187 MPa and the fatigue ratio to the tensile strength was found to be σ/σB =6-9%. The fracture surface morphology of failed specimens observed by SEM showed evidently three main regions as follows: 1) flat area corresponding to the crack initiation and the early growth stages up to penetrate the thickness of the film specimen. 2) rough area with a lot of chevron patterns corresponding to the stable propagation as the penetrated fatigue crack. 3) relatively plain area with vein patterns peculiar to the static fracture surface of amorphous metals.