Normal and abnormal grain growth in fine-grained Nd-Fe-B sintered magnets prepared from He jet milled powders

Bittner, F.; Woodcock, T.G.; Schultz, L.; Schwöbel, C. A.; Gutfleisch, Oliver; Zickler, Gregor A.; Fidler, J.; Üstüner, K.; Katter, M.

doi:10.1016/j.jmmm.2016.10.139

Cited by 33 publications

(13 citation statements)

References 44 publications

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“…Two HRE free powders (Nd,Pr) 14.9 (Fe,Co) 78.5 T 1.0 B 5.6 (magnet A) and (Nd,Pr) 16.9 (Fe,Co) 76.6 T 1.0 B 5.5 (Magnet B) with T = Al, Ga, Cu were jet milled in He atmosphere resulting in a particle size of 1.5 m and an average grain diameter < 2 m after sintering and annealing treatment [9]. After the sintering at the optimized temperatures of 980 ∘ C (magnet A) and 920 ∘ C (magnet B) and annealing at 500 ∘ C a density of 7.59 g/cm 3 and 7.58 g/cm 3 for magnets A and B, respectively, was achieved.…”

Section: Methodsmentioning

confidence: 99%

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

Zickler

Fidler

Bernardi³

et al. 2017

Advances in Materials Science and Engineering

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The nanoanalytical high resolution TEM/STEM investigation of the intergranular grain boundary phase of anisotropic sintered and rapidly quenched heavy rare earth-free Nd-Fe-B magnet materials revealed a difference in composition for grain boundaries parallel (large Fe-content) and perpendicular (low Fe content) to the alignment direction. This behaviour vanishes in magnets with a high degree of misorientation. The numerical finite element micromagnetic simulations are based on the anisotropic compositional behaviour of GBs and show a decrease of the coercive field with an increasing thickness of the grain boundary layer. The magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries parallel to thec-axis and secondly as Néel domain wall perpendicular to thec-axis into the adjacent hard magnetic grains. The increasing misalignment of grains leads to the loss of the anisotropic compositional behaviour and therefore to an averaged value of the grain boundary composition. In this case the simulations show an increase of the coercive field compared to the anisotropic magnet. The calculated coercive field values of the investigated magnet samples are in the order ofμ0HcJ=1.8 T–2.1 Tfor a mean grain boundary thickness of 4 nm, which agrees perfectly with the experimental data.

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Section: Methodsmentioning

confidence: 99%

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

Zickler

Fidler

Bernardi³

et al. 2017

Advances in Materials Science and Engineering

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“…Usually, the composition of GB layers in Nd-Fe-B-based permanent magnets is measured by EDS in TEM and SEM [6,[41][42][43]. In these measurements, the content of main metallic elements is mostly determined [6,43], and only very seldom that of oxygen [6,41,43]. For example, the minima of iron and cobalt concentrations as well as maxima of oxygen, fluorine, neodymium and praseodymium concentrations were observed by EDS in the ~4 nm thin GB area [43].…”

Section: Gb Oxides In Nd-fe-b-based Alloysmentioning

confidence: 99%

Grain boundaries in Nd-Fe-B-based alloys

et al. 2020

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In this review we consider the microstructure of grain boundaries (GBs) in the Nd-Fe-B-based alloys for permanent magnets. It is generally accepted that the unique hard magnetic properties of such alloys are controlled by the thin layers of a Nd-rich phase in Nd 2 Fe 14 B / Nd 2 Fe 14 B GBs. These GB layers ensure the magnetic isolation of Nd 2 Fe 14 B grains from each other. It is generally supposed that such GB layers contain metallic Nd or Nd-rich intermetallic compounds. However, the commercial Nd-Fe-B-based permanent magnets frequently contain the tangible amount of neodymium oxide Nd 2 O 3 in the triple junctions between Nd 2 Fe 14 B grains. In this review we show that oxide layers are also present in the GBs in Nd-Fe-B-based permanent magnets. The Nd-based phase in GBs can form continous layers between Nd 2 Fe 14 B grains (this case is called complete wetting). It corresponds to the zero contact angle between GB and Nd-rich phase. If the contact angle is non-zero, the Nd-based phase forms the chain of particles in the GB. In turn, if the GB between these particles is "dry", this case is called the incomplete wetting. If the GB between the Nd-rich particles contains the thin layer of a Nd-rich phase (either metallic or oxide), this case is called the pseudo-incomplete (or pseudo-partial) GB wetting.

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“…As curvas de desmagnetização dos ímãs produzidos são apresentadas na No caso dos ímãs produzidos com 30 minutos de moagem, este "joelho" pode ter sua origem na heterogeneidade do tamanho de partícula devido ao tempo insuficiente de moagem, produzindo uma distribuição de grãos muito ampla [37][38][39][40].…”

Section: Caracterização Magnéticaunclassified

“…Outro fator é a própria granulometria no pó produzido, que não é adequada à temperatura de sinterização, favorecendo o fenômeno de crescimento anormal de grãos, produzindo também uma distribuição muito ampla de diâmetros de grãos. [37][38][39][40].…”

Section: Caracterização Magnéticaunclassified

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Influência dos parâmetros de processamento na microestrutura e nas propriedades magnéticas de ímãs permanentes de (Nd,Pr)FeB

Fim¹

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Normal and abnormal grain growth in fine-grained Nd-Fe-B sintered magnets prepared from He jet milled powders

Cited by 33 publications

References 44 publications

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

Grain boundaries in Nd-Fe-B-based alloys

Influência dos parâmetros de processamento na microestrutura e nas propriedades magnéticas de ímãs permanentes de (Nd,Pr)FeB

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