Microstructure Formation in Strip-Cast RE-Fe-B Alloys for Magnets
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Microstructure Formation in Strip-Cast RE-Fe-B Alloys for Magnets KAZUHIKO YAMAMOTO, MASASHI MATSUURA, and SATOSHI SUGIMOTO During the manufacturing of sintered NdFeB magnets, it is well known that the microstructure of the starting alloy has a strong influence on the processing and the magnetic properties of the product. In this study, we clarify the microstructure formation in strip-cast rare earth (R)-Fe-B alloys used to produce magnets. The microstructure of the alloy surface in contact with the cooling roll and its cross-section were observed using laser microscopy, field emission electron microprobe analysis, and transmission electron microscopy. The orientations of crystal grains were determined by X-ray diffraction and electron backscatter diffraction analyses. Petal-shaped structures were found to cover the alloy surface in contact with the cooling roll, each consisting of a central nucleation region and radially grown Nd2Fe14B dendritic structures. The nucleation region, consisting of a ‘‘disc’’ and ‘‘predendrites’’, occurs in the super-cooled region of the contact area between the cooling roll and melt. In the disc region, spherical Nd2Fe14B particles
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