Compaction of bulk ferromagnetic Fe 80 P 13 C 7 amorphous alloys
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When bulk ferromagnetic Fe80 P13C7 amorphous rods of approximately 2-mm diameter are compacted together in a hot press, a variety of different microstructures, depending on the experimental conditions, are produced. The most intriguing microstructure is that two different bulk amorphous rods can be fused together perfectly at a temperature of 683 K and under a pressure of 2.5 to 4 GPa for a period of 5 min.
Conventionally, amorphous metals are prepared by rapid melt quenching.1,2 Consequently, one dimension of the as-formed specimens is in general very thin, about 50 m in thickness, to facilitate heat removal. Fe-based amorphous alloys possess attractive soft magnetic properties and are functional materials for motors, transformers, high-frequency transducers, and so on. During the past few years, there have been significant advances2,3 in the synthesis of bulk metallic glasses and Fe-based ferromagnetic amorphous rods3 with a diameter as large as a few millimeters can be produced. In practical applications it is desirable to have their physical dimensions even larger. There is a standard metallurgical technique to prepare large chunks of materials, which is powder sintering, a method that is commonly used in the manufacturing of nanostructured materials from nanometer-sized powders.4,5 Earlier, Kojima et al.6 and Louzguine et al.7 employed it to sinter amorphous powders that were prepared by a rapid melt quenching at an elevated temperature and under high pressure. The density of the amorphous compact can be better than 98.3% of the theoretical value. Recently, it was found8 that molten Fe80 P13C7 9 can be quenched to bulk ferromagnetic glass in the shape of rods with a maximum diameter of 2 mm. However, it is imperative to prepare even larger specimens of this kind for direct use. We report here on compaction experiments of bulk ferromagnetic amorphous Fe80 P13C7 alloy rods with a diameter of approximately 2 mm, whereas in earlier studies of the compaction of Fe-based alloys, the starting materials were amorphous powders. Fe80 P13C7 ingots were prepared from Fe granules and C flakes, and FeP powders. For convenience, the FeP powders were first melted into ingots. Then the right proportion of Fe granules and C flakes and FeP ingots to form a Fe80 P13C7 specimen were put in a clean fused J. Mater. Res., Vol. 16, No. 10, Oct 2001
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silica tube and alloyed in a radio-frequency induction furnace under Ar atmosphere. Most of the as-prepared raw Fe80 P13C7 specimens in ingot shape had a diameter of approximately 6 mm. For completeness, the synthesis method of preparing bulk ferromagnetic Fe80 P13C7 amorphous alloys, which can be divided into two parts, is briefly introduced here. In the first part,10 a raw Fe80 P13C7 ingot and anhydrous B2O3 were put in a clean fused silica tube of vacuum approximately 10−3 torr and at a temperature appproximately 200 K above the liquidus Tl of Fe80 P13C7 (Tl ⳱ 1232 K). The B2O3, called fluxing agent, served to remove heterophase im
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