Abstract:
Nanostructured Nd–Fe–B-type materials produced by melt-spinning (MS) are used in a variety of applications in the electronics, automotive, and sensor industries. The very rapid MS process leads to flake-like powders with metastable, nanoscale, Nd2Fe14B grains. These powders are then formed into net shaped, isotropic, polymer-bonded magnets, or they are hot formed into fully dense, metallic magnets that are isotropic and anisotropic. These fully dense magnets are usually produced with a conventional hot press without the inclusion of additives before the hot pressing. As a result, their properties, particularly the coercivity (Hci), are insufficient at automotive-relevant temperatures of 100–150 °C since the material Hci has a large temperature coefficient. In this study, we instead add a thin layer of TbF3 to the melt-spun ribbons before their hot consolidation to enhance the coercivity through a diffusion-based, partial substitution of the Nd by Tb. This effect is accomplished by applying extremely rapid, spark- plasma sintering to minimize any growth of the nanoscale Nd2Fe14B grains during consolidation. By using field-emission gun scanning electron microscope (FEG-SEM) with the energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscope (HRTEM) we confirmed the formation of the core-shell-type microstructure, which results in increased coercivity.
The result is a magnet with very high-coercivity with drastically reduced amounts of heavy rare earth that is suitable for high-temperature applications. This work clearly demonstrates how rapidly formed, metastable states can provide us with properties that are unobtainable with conventional techniques.
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