Texture induced magnetic anisotropy in Fe-Nd-B magnet prepared via rapid solidification and hot extrusion techniques
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Texture Induced Magnetic Anisotropy in Fe-Nd-B Magnet Prepared via Rapid Solidification and Hot Extrusion Techniques CHOONGJIN YANG (a)
(b) Fig. 5 - - Microstructure of the composite after 1 h at 800 ~ creased Si and AI4C3.
showing in-
liquidus is a very convenient method, and should be sufficiently accurate for composites with normal levels of reinforcement, e.g., greater than 10 vol pct. The accuracy of the method can be assessed in principle, by quantitative metallography, measuring the volume fraction of silicon phase. The aluminum carbide content can also be determined, but the silicon phase is much easier to resolve, as seen from Figure 5. The silicon content can atso be measured by chemical analysis, after passing the molten composite through a ceramic filter to remove the particulate, but this can be done only for low temperatures and short reaction times because the fluidity of the melt decreases rapidly with increasing A14C3 formation. A few experiments of the latter type have been carried out and gave results in good agreement with the DSC data, but improved chemical analytical techniques need to be developed to investigate a broader temperature range. REFERENCES 1. R. Warren and C-H. Andersson: Compos., 1984, vol. 15, pp. 101-11. 2. T. Iseki, T. Kameda, and T. Maruyama: J. Mater. Sci., 1984, vol. 19, METALLURGICALTRANSACTIONS A
There are three basic criteria that have to be met by Fe (or Co)-R (rare earth) magnets to achieve optimum squareloop behavior in the demagnetization regime and hence high energy products: (1) the material must consist of an assembly of fine particles in order to possess high coercivities, He, and He; (2) the particles must exhibit microscopic magnetic anisotropy; i.e., they must have a preferred easy axis of magnetization; and (3) the microscopically anisotropic particles must be capable of being aligned with their easy axes all pointing in the same direction in order to achieve high Br. Through the rapid solidification technology, the first criterion can be met in the Fe-R-B system; while the intrinsic characteristics of the Fe-R-B alloys automatically fulfill the second criterion. Recently a hot extrusion technique has been reported to be employed to satisfy the third criterion.t~'2~ The present report examines the magnitude and distribution of normal strain under three different die openings, i.e., of circle, square, and rectangle, respectively, and their effects on evolution of texture in the magnet prepared by hot extrusion of rapidly solidified melt spun powders. At the same time, the anisotropic properties found in the extruded Fe-Nd-B based magnet containing HfB 2 as a grain refinertlj have been characterized. The proprietary melt spinning technique was employed to produce rapidly quenched narrow (I0/zm thick, 100/~m wide) and short amorphous powders (about 60 mesh), using a substrate speed of 44 m/sec. In this process, the molten metal is extracted by a knife-edged rotating wheel and converted into short filaments solidified at a uniform rate of 106 ~ Amorphous mate
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