DETERMINATION AND IDENTIFICATION OF ATOMIC STRUCTURE OF AMORPHOUS ALLOYS

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High resolution electron microscopy (interference image microscopy), field-ion microscopy and high voltage electron microscopy were successfully used in combination with X-ray and/or electron diffraction method to investigate the structure and the thermal stability of liquid-quenched Fe-P, Fe-P-C, Fe-B-Si and Ni-B-Si alloys in conjunction with quenching methods and preparation conditions. The untilted interference images and field-ion images of the liquid-quenched alloys prepared by drum-quenching method and by roller-quenching method at a fast quenching rate yielded no evidence of the existence of microcrystallites larger than several atomic spacings in diameter. However, a periodical fringe-like contrast indicating the existence of a regular atomic arrangement was locally observed in the alloys quenched at slower quenching rate. A periodical fringe-like contrast was also observed in the regions adjacent to the crystalline phase in the amorphous alloys partially crystallized by heating. Furthermore, a circular arrangement of image spots indicating the existence of a regular atomic arrangement was also observed locally in the field-ion image of the tipped specimen heated at a temperature below the crystallization temperature. These regions, in which the periodical fringe-like contrast or the circular arrangement of image spots were observed, yielded only halo rings in their diffraction patterns. Therefore, to characterize amorphous alloys prepared by various methods under different conditions or to identify those amorphous alloys, the directer methods such as high resolution electron microscopy and/or field-ion microscopy must be used in combination with X-ray or electron diffraction method which has been usually used in most cases so far. When thin foil specimens of liquid-quenched Fe-P, Fe-P-C and Ni-B-Si amorphous alloys were heated in-situ under the irradiation of 400keV electrons in a high voltage electron microscope, two types of electron irradiation effect were observed; one is an acceleration of crystallization, which was observed in the Ni-B-Si amorphous alloy, and the other is a retardation of crystallization, which was observed in the Fe-P and Fe-P-C amorphous alloys. Pole figure determinations suggest that no preferred orientation was developed appreciably in the crystallization processes of the liquid-quenched Fe-P-C amorphous alloy and also the cold-rolled sheet of this alloy. In the case of room temperature deformation, the load-elongation curves of the Fe-P-C and Fe-B-Si alloys prepared at the faster quenching rate indicate some deviation from the linearity well below the fracture point. While in the case of the alloys which were prepared at the slower quenching rate and which exhibited a periodical fringe-like contrast in the untilted interference images, the load-elongation curves were almost straight and practically no deviation was observed up to fracture. Scanning electron microscope observations of the fractured surfaces revealed that the shear displacement occurred in the alloys prepared at the faster quenching rate but not in the alloys prepared at the slower quenching rate. After a series of loading-unloading stress cycles where the maximum load of each stressing cycle was gradually increased, the load-elongation curves of the Fe-P-C and Fe-B-Si alloys prepared at the faster quenching rate became straighter and the deviation from the linearity was much smaller even at the fracture point.
東北大学の論文

DETERMINATION AND IDENTIFICATION OF ATOMIC STRUCTURE OF AMORPHOUS ALLOYS

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