High-coercivity ultrafine-grained anisotropic Nd–Fe–B magnets processed by hot deformation and the Nd–Cu grain boundary diffusion process
TL;DR: In this article, the grain boundary diffusion process using an Nd70Cu30 eutectic alloy has been applied to hot-deformed anisotropic Nd-Fe-B magnets, resulting in a substantial enhancement of coercivity, at the expense of remanence.
About: This article is published in Acta Materialia.The article was published on 2013-10-01. It has received 246 citations till now. The article focuses on the topics: Coercivity & Grain boundary diffusion coefficient.
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TL;DR: In this article, the dependence of the coercivity of hot-deformed anisotropic Nd-Fe-B magnets on grain size has been studied by processing the magnets at different temperatures.
166 citations
TL;DR: In this article, the authors presented the results of a project for the U.S. Department of Energy, Office of Basic Energy Sciences, under Award No. DE-SC0005051 and DE-FG02-06ER46275.
Abstract: Deutsche Forschungsgemeinschaft (Project No. BE 2464/10-3), the EU-FP7 project “NANOPYME” (310516), and the EU Horizon-2020 project “AMPHIBIAN” (720853). M. R. E. was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Award No. DE-SC0005051. F. B. thanks Andreas Ulbricht for fruitful discussions over the many years. C. L. was funded by the U.S. Department of
Energy through the University of Minnesota Center for Quantum Materials under DE-FG02-06ER46275 and DESC-0016371. S. D. acknowledges financial support from the
German Research Foundation (DFG Emmy Noether Grant No. DI 1788/2-1).
164 citations
Cites methods from "High-coercivity ultrafine-grained a..."
...…microscopy, electron backscattering diffraction, threedimensional atom-probe analysis, Lorentz and Kerr microscopy, or atomistic and continuum micromagnetic simulations (Gutfleisch et al., 2011; Hono and Sepehri-Amin, 2012; Woodcock et al., 2012; Liu et al., 2013; Sepehri-Amin et al., 2013, 2015)....
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TL;DR: The application of expansion constraint during the grain-boundary diffusion process using Nd70Cu30 eutectic alloy minimizes the remanence loss for the coercivity enhancement by optimizing the volume fraction of the Nd(Cu)-rich non-ferromagnetic intergranular layer as mentioned in this paper.
127 citations
TL;DR: In this article, the authors showed that the degradation of thermal stability of coercivity in the (Nd,Pr) 2 Fe 14 B regions is due to the large temperature dependence of anisotropy field in the Nd 2,Pr 2 Fe14 B regions, which is considered to cause a slight decrease in Curie temperature.
125 citations
TL;DR: In this paper, the authors found that the 2:14:1 phase can be improved by sintering above the melting point of this papere2 phase, which promotes densification of the magnet and the formation of continuous and smooth grain boundary (GB) phases.
124 citations
References
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TL;DR: In der krystallographischen Literatur der letzten Zeit erscheinen mehr und mehr Arbeiten, welche dem gegenseitigen Verhältnisse des Krystalles and des Mediums, in welchem er sich bildet, gewidmet sind.
Abstract: In der krystallographischen Literatur der letzten Zeit erscheinen mehr und mehr Arbeiten, welche dem gegenseitigen Verhältnisse des Krystalles und des Mediums, in welchem er sich bildet, gewidmet sind. Besonders erfolgreich sind in dieser Hinsicht die Arbeiten von B e c k e gewesen. Seine Abhandlung über die Aetzflguren und die Auflösung des Fluorits veranlasste mich, die vorliegende Untersuchung zu beginnen. Das Verhältniss des Krystalles zu seiner Mutterlauge ist dreierlei Art. Der Krystall kann in ihr wachsen oder sich auflösen oder unverändert bleiben, je nach dem Grade der Sättigung der Lösung. Die Fähigkeit des Wachsens unterscheidet wesentlich die Krystalle von den amorphen Körpern. Dabei versteht man unter dem Wachsthume eine solche Vergrösserung des Volums, welche weder von einer Veränderung
1,803 citations
TL;DR: In this article, the Wulff construction for the equilibrium shape of a small particle and the relations between atomic models of crystal surfaces and the surface free energy function used in this construction are discussed.
Abstract: Although the interpretation of experiments in such fields as the shapes of small particles and the thermal etching of surfaces usually involves problems of kinetics rather than mere equilibrium considerations, it is suggested that a knowledge of the relative free energies of different shapes or surface configurations may provide a useful perspective. This paper presents some theorems on these relative free energies which follow from the Wulff construction for the equilibrium shape of a small particle, and some relations between atomic models of crystal surfaces and the surface free energy function used in this construction. Equilibrium shapes of crystals and of noncrystalline anisotropic media are classified, and it is pointed out that the possibilities for crystals include smoothly rounded as well as sharp-cornered forms. The condition is formulated for thermodynamic stability of a flat crystal face with respect to formation of a hill-and-valley structure. A discussion is presented of the limitations on the applicability of the results imposed by the dependence of surface free energy on curvature; and it is concluded that these limitations are not likely to be serious for most real substances, though they are serious for certain idealized theoretical models.
1,208 citations
TL;DR: The formation of continuous thin layers of a Ndrich amorphous phase surrounding Nd 2 Fe 14 B grains is the key microstructural feature of high-coercivity Nd-Fe 14 B magnets.
511 citations
TL;DR: In this article, a detailed analysis of the temperature dependence of H c is given on the basis of the predictions of micromagnetic theories for pinning and nucleation mechanisms, and it is shown that the nucleation theory leads to a coherent interpretation of all relevant properties of Hc than the pinning theory if the effects of misaligned grains, local stray fields and reduced anisotropies in grain boundaries are taken into account.
493 citations
TL;DR: In this paper, a new method is described which produces fully dense, well aligned Nd•Fe•B magnets from rapidly quenched ribbons, achieved by hot pressing at ∼15 kpsi in argon at 700 °C, and a second hot press in a larger die cavity to allow deformation transverse to the press direction (die upsetting).
Abstract: A new method is described which produces fully dense, well‐aligned Nd‐Fe‐B magnets from rapidly quenched ribbons Full density is achieved by hot pressing at ∼15 kpsi in argon at 700 °C A second hot press in a larger die cavity to allow deformation transverse to the press direction (die upsetting) introduces a preferred magnetization direction parallel to the press direction Energy products of 40 MGOe (Br/Hci=135 kG/11 kOe) have been generated by this method
436 citations