Magnetic and microstructural investigation of high-coercivity net-shape Nd–Fe–B-type magnets produced from spark-plasma-sintered melt-spun ribbons blended with DyF3

• Published in: Journal of magnetism and magnetic materials Vol. 403; pp. 90 - 96
• Main Authors: Žagar, Kristina, Kocjan, Andraž, Kobe, Spomenka
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-2016
• Subjects: Coercivity enhancement; Melt-spinning; Microstructures; Permanent magnets; Spark-plasma sintering; Permanent magnets; Melt-spinning; Microstructures; Coercivity enhancement; Spark-plasma sintering
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2015.11.082

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 prior to 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 DyF3 to the melt-spun ribbons prior to their hot consolidation in order to enhance the coercivity through a diffusion-based, partial substitution of the Nd by Dy. This is accomplished by applying extremely rapid, spark-plasma sintering to minimize any growth of the nanoscale Nd2Fe14B grains during consolidation. The result is a very high-coercivity magnet with drastically reduced amounts of heavy rare earths 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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•We produced high coercivity magnets with drastically reduced amounts of HRE.•Microstructural analysis was conducted of the “free” and “wheel” side of Dy-treated Nd2Fe14B ribbons.•Dy-diffusion mechanism into ribbons depending on processing parameters is shown.