共晶粒界拡散プロセスによる熱間加工ネオジム系永久磁石の高性能化

筑波大学 (University of Tsukuba)201

RE-Fe-B系熱間加工磁石の高性能化に関する研究

筑波大学 (University of Tsukuba)201

Generation and characterization of anisotropic microstructures in rare earth-iron-boron alloys

The automotive industry is currently being directed toward electrification of their fleets. In order to provide these hybrid or electric vehicles, lightweight high torque electric motors are needed. Permanent magnet (PM) brushless motors have been identified as the preferred motors for these applications. In order to effectively provide these motors, cost-effective high strength PMs are needed. The use of polymer bonded PMs is one method to reduce processing costs, but performance is decreased unless anisotropic PMs can be formed. New processing methods to form anisotropic mixed rare earth (MRE)-iron-boron PM particulate were studied in this work. Two primary processing routes were identified and investigated: controlled devitrification through application of uniaxial pressure and rapid directional solidification utilizing a segregating additive. In addition, further control of the melt-spinning process was achieved through control of wheel surface temperature and finish. Controlled devitrification was found to produce an anisotropic, nanocrystalline microstructure, as observed through TEM and XRD studies. A high defect density within the structure, unprecedented in RE2Fe14B microstructures, was observed. It is surmised that the defects cause soft magnetic behavior. Stabilization of a columnar, textured microstructure was achieved through the utilization of moderate wheel speeds during melt-spinning, in combination with minor additions of Ag to the alloy. The texture was seen to be altered from that typically seen in RE2Fe14B alloys melt-spun at low-to-moderate wheel speeds. It was observed that this occurs through a modification in the solidification pathway, catalyzed by the addition of Ag. In addition to the altered texture, the presence of fine precipitates within the matrix and varying interdendritic phases was observed. Alteration of wheel surface temperature and surface finish was seen to have significant effects on the ability to form amorphous material in Nd2Fe14B + TiC alloys. Counter to the predictions of several theoretical models, increased wheel surface temperatures were seen to increase the glassy fraction. Additionally, utilizing coarser abrasives to finish the wheel surface resulted in greater amorphous fractions. It is proposed that the changes are correlated with alteration of wetting behavior between the wheel and the melt. The work presented here provided promising directions for the formation of anisotropic particulate suitable for use in polymer-bonded permanent magnets

The Sm-Fe- V based 1:12 permanent magnets.

137 p.Criticality of the rare earth (RE) metals has encouraged materials researchers to explore RE-lean/free alternatives to Nd-Fe-B and Sm-Co permanent magnets. In this context, the Sm-based compounds with ThMn12 (1:12) structure exhibiting intrinsic magnetic properties comparable to that of Nd2Fe14B compounds are considered as one of the alternatives. This thesis aims to develop Sm-based 1:12 magnets with magnetic properties comparable to Nd-Fe-B magnets without using critical raw metals such as Nd, Dy, Tb, Co and with reduced use of Sm. For this purpose, the studies are divided into three parts. The first part of the investigations focuses on the 1:12 phase stabilization and improvement of the intrinsic magnetic properties in the.SmFe12-xVx (x = 2, 1.5, 1.0, 0.5) systems. The second part deal with transferring the intrinsic properties into extrinsic properties, and the main task consisted in developing coercivity on stoichiometric and off-stoichiometric SmFe10V2 alloys. Two approaches were used to achieve this goal (i) through grain size refinement using powder metallurgy route and rapid solidification, and (ii) via bulk magnetic hardening by precipitation of the eutectic Sm-La phase. The third part is devoted to the consolidation of the mechanical milled powders into bulk magnets using hot compaction and hot deformation processes. During this process, the bulk materials developed the proper microstructure and thus the magnetic properties. A maximum coercivity of 1.06 T with M3T = 0.59 T, Mr = 0.42 T and (BH)max = 28 kJ m-3 was obtained in Sm12Fe73V15 isotropic hot compacted. The Curie temperature was measured to be 330°C and the temperature coefficients of remanent magnetization and coercivity were 0.14% C-1 and 0.39% C-1, respectively. Minor hysteresis loops indicate a coercivity mechanism similar to that of the nanocrystalline Nd-Fe-B magnets. Magnets with modified compositions Sm-Fe-(V,M) (M = Ti, Mo, Cu) were synthesized in order to investigate the effect on the magnetic properties of Sm12Fe73V15 when V was reduced or partially substituted by another transition metal. All the mechanically milled powders were successfully consolidated into fully-dense magnets. The most striking result was that magnets with compositions Sm12Fe76.5V11.5 and Sm12Fe73V7.5Mo7.5 developed a texture perpendicular to the deformation direction

The Sm-Fe- V based 1:12 permanent magnets.

137 p.Criticality of the rare earth (RE) metals has encouraged materials researchers to explore RE-lean/free alternatives to Nd-Fe-B and Sm-Co permanent magnets. In this context, the Sm-based compounds with ThMn12 (1:12) structure exhibiting intrinsic magnetic properties comparable to that of Nd2Fe14B compounds are considered as one of the alternatives. This thesis aims to develop Sm-based 1:12 magnets with magnetic properties comparable to Nd-Fe-B magnets without using critical raw metals such as Nd, Dy, Tb, Co and with reduced use of Sm. For this purpose, the studies are divided into three parts. The first part of the investigations focuses on the 1:12 phase stabilization and improvement of the intrinsic magnetic properties in the.SmFe12-xVx (x = 2, 1.5, 1.0, 0.5) systems. The second part deal with transferring the intrinsic properties into extrinsic properties, and the main task consisted in developing coercivity on stoichiometric and off-stoichiometric SmFe10V2 alloys. Two approaches were used to achieve this goal (i) through grain size refinement using powder metallurgy route and rapid solidification, and (ii) via bulk magnetic hardening by precipitation of the eutectic Sm-La phase. The third part is devoted to the consolidation of the mechanical milled powders into bulk magnets using hot compaction and hot deformation processes. During this process, the bulk materials developed the proper microstructure and thus the magnetic properties. A maximum coercivity of 1.06 T with M3T = 0.59 T, Mr = 0.42 T and (BH)max = 28 kJ m-3 was obtained in Sm12Fe73V15 isotropic hot compacted. The Curie temperature was measured to be 330°C and the temperature coefficients of remanent magnetization and coercivity were 0.14% C-1 and 0.39% C-1, respectively. Minor hysteresis loops indicate a coercivity mechanism similar to that of the nanocrystalline Nd-Fe-B magnets. Magnets with modified compositions Sm-Fe-(V,M) (M = Ti, Mo, Cu) were synthesized in order to investigate the effect on the magnetic properties of Sm12Fe73V15 when V was reduced or partially substituted by another transition metal. All the mechanically milled powders were successfully consolidated into fully-dense magnets. The most striking result was that magnets with compositions Sm12Fe76.5V11.5 and Sm12Fe73V7.5Mo7.5 developed a texture perpendicular to the deformation direction

Magnetic Functional Materials: Synthesis, Characterization and Application

Magnetic functional materials are widely used in energy, information, and materials science and technology. There are many kinds of magnetic functional materials, and their progress is rapid. Magnetic functional materials have attracted a great deal of attention regarding their applications. Magnetic behaviors are widespread in a variety of materials, such as metals, ceramics, organics, and emerging 2D materials. The applications of magnetic materials include memories, sensors, magnetic refrigeration, drug delivery, electrochemistry, environmental protection, energy storage, and more. This Special Issue, “Magnetic Functional Materials: Synthesis, Characterization and Application”, addresses existing knowledge gaps and aids advance deployment of magnetic functional materials. It consists of nine peer-reviewed papers and one editorial that cover a range of subjects and applications related to magnetic functional materials

The processing and characterisation of recycled NdFeB-type sintered magnets

A study of the processing and characterisation of sintered NdFeB magnets made from recycled feed stock was undertaken. Initially the hydrogen decrepitated (HD) powder was investigated using two different milling techniques. The powders were analysed with optical microscopy, with the aid of a magnetic field. It was found that with light milling the HD powder breaks up to a similar particle size to that of the grain size of the starting material. A data logging system was built to investigate the desorption behaviour of green compacts during sintering. Desorption traces showed desorption from the matrix phase and the intergranular Nd-rich phase. The start of desorption was seen to shift to lower temperatures as the mean particle size of the green compact was reduced. For the processing route used in this work intergranular additions of neodymium hydride were required to increase the density and magnetic properties. To investigate the oxidation behaviour of lightly milled HD powder, powder was exposed to air for varying times. The exposed powder was aligned pressed and sintered. The Nd-rich desorption peak reduced with exposure time, the density and magnetic properties also reduced. Post exposure additions of Intergranular neodymium hydride to the powder recovered density and magnetic properties

Recycling process of permanent magnets by polymer binder using injection molding technique

Seltene Erden-Elemente (REE) werden aufgrund ihrer technologischen Bedeutung und geopolitischen Versorgungskriterien als kritische Metalle eingestuft. Sie werden in einem breiten Spektrum von Anwendungen eingesetzt, einschließlich der Herstellung von Magneten, Batterieelektroden, Katalysatoren und Polierpulver. Viele dieser Anwendungen sind wichtig für die sog. „grünen“ Technologien. Dauermagneten sind hinsichtlich der Marktgröße die wichtigste Anwendung insbesondere für Neodym-, Praseodym-, Dysprosium- und Terbium-Magnete, die in NdFeB-Magneten verwendet werden. Die Nachfrage nach Seltenerdelementen für die Herstellung von Magneten nimmt zu und es wird erwartet, dass sich dieser Trend in den kommenden Jahren fortsetzt. Um die mit der Nachfrage verbundenen Risiken zu verringern, wurden Maßnahmen zur Entwicklung von Recyclingtechnologien zur Wiederverwendung von NdFeB aus Magneten ergriffen. Während der industrielle NdFeB-Schrott bereits zurückgewonnen wird, ist das Recycling von Magneten aus Altprodukten noch weitergehend auf Labor- und Pilotprojekte beschränkt. Diese Abhandlung stellt die Ergebnisse der Materialanalyse vor, die die Möglichkeit bestätigen, magnetische Materialien durch die Einarbeitung in eine Polymermatrix zu recyceln und mittels Spritzgussprozess vorzubereiten. Kern der vorliegenden Dissertation ist die Frage, wie der geschlossene Kreislauf und das Recyclingverfahren von Neodynium Magneten aus Elektroschrott gestattet sein soll. Um diese Frage zu beantworten, sind folgende Aspekte relevant: • Die Wahl der Technologien/Prozesse, die für das Recycling eingesetzt werden. • Nachweis der Wiederverwendung von Neodym-Magneten, die aus WEEE (Waste of Electrical and Electronic Equipment) gewonnen sind. • Herstellung und Analyse von Polymer/Magnet- Compound. • Einfluss der Magnetpartikel, abhängig von ihrer Anzahl und Größe, auf die Viskosität und Fließverhalten des Materials während des Spritzgussprozess. • Analyse des Einflusses der Restmagnetisierung auf das Fließverhalten und einer gezielten Anordnung von magnetischen Partikeln im Bauteil. • Technisch-ökonomische Analyse, die entscheidend dazu beitragen wird, ob und in welchem Ausmaß die Einführung des Prozesses erreichbar ist und damit geschlossene Kreisläufe möglich sind. Auf der Grundlage einer umfangreichen Analyse wurden die optimalen Prozessparameter und die Spritzgussmöglichkeiten des verwendeten Materials vorgestellt. Die Nachfrage nach NdFeB-Magneten in Motoranwendungen wächst und wird in den nächsten Jahren voraussichtlich noch zunehmen. Vor allem die Nachfrage nach E-Bike und E-Autos gewinnt an Bedeutung. Infolgedessen wird die Nachfrage nach schweren Seltenen Erden steigen, was die Entwicklung von Recyclingsystemen für diese Materialien erforderlich macht.Rare earth elements (REE) are classified as critical metals due to their technological importance and geopolitical supply criteria. They are used in a wide range of applications, including the manufacture of magnets, battery electrodes, catalysts, and polishing powders. Many of these applications are important for so-called "green" technologies. Permanent magnets are the most important application in terms of market size, particularly for neodymium, praseodymium, dysprosium, and terbium magnets used in NdFeB magnets. The demand for rare earth elements for the production of magnets is increasing and this trend is expected to continue in the coming years (Langkau S. 2020; Li J. 2020; Goodenough K.M. et al. 2018). To mitigate the risks associated with that demand, have been taken to develop recycling technologies to reuse NdFeB magnets. While industrial scrap is already being recovered, recycling of magnets from end-of-life products is still further limited to laboratory and pilot projects. The following work presents the results of the material analysis, which confirm the possibility to recycle magnetic materials by using a polymer matrix. The main goal of this dissertation is the question of how the closed-loop and recycling process of neodymium magnets from electronic waste should be designed. To answer this question, the following aspects are relevant: • The choice of technologies/processes used for recycling and processing. • Evidence of reuse of neodymium magnets obtained from WEEE (Waste of Electrical and Electronic Equipment). • Process flow analysis and final product evaluation (polymer/magnet compound). • The effect of magnetic particles characteristics (size, distribution, and contribution) on the viscosity and flow behavior of the material during the injection molding process. • Analysis of residual magnetization on the flow behavior and a targeted arrangement of magnetic particles in the component. • Technical-economic analysis, which decisively contributes to whether and to what extent the introduction of the process is achievable. Based on an extensive analysis, the optimal process parameters and the maximum injection possibilities of the material used is discussed along the whole processing line. The demand for NdFeB magnets in motor applications is growing and is expected to increase in the coming years. In particular, the demand for e-bikes and e-vehicles is gaining importance (Kampker A. et al. 2021; Pollák F. 2021; Flores P.J 2021). As a result, the demand for heavy rare earths will increase, necessitating the development of recycling systems for these materials, where this thesis is one basic concept to close the loop

Demagnetizing and hardening mechanisms in Nd-Fe-B and Sr-hexaferrite permanent magnets

In the first part of this work, the microstructural influence on magnetic properties Sr-hexaferrites is investigated. Using a Magnetic Force Microscope (MFM) the domain evolution during magnetization from the Thermally Demagnetized State (TDS) and DC field Demagnetized State (DCD) and during demagnetization was investigated in-situ. A surface magnetization was determined from the MFM contrast that quantitatively matched the bulk magnetization determined by Superconducting Quantum Interface Device (SQUID). For the surface magnetization it was found that smaller grains below the critical single domain size reversed their magnetization from Single Domain State (SDS) to the reversed SDS, while larger grains form an intermediate Multi Domain State (MDS). Using a series of minor loops it was determined that the presence of MDS in the bulk is neglectable. An in-depth analysis of core shell structured Nd-Fe-B grains was carried out using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), optical Kerr microscopy and MFM. While the core consisted of pure Nd2Fe14B the shell, the composition of the shell was (Nd1-xDyx)2Fe14B. The composition and morphology of the grain boundary was analyzed using TEM. Using MFM the magnetic contrast of core and shell due to the lower saturation magnetization of the Dy substituted species could be correlated to the chemical contrast observed by SEM. The demagnetization of core and shell was observed under in-situ condition using MFM and Kerr microscopy. The results show a uniform demagnetization across core and shell. The time resolution of the Kerr microscope of 43 frames per second is not large enough to resolve an intermediate domain state between SDS and stable MDS within the 23 ms between two frames. In a subsequent micromagnetic simulation the nucleation site was shown to lie either at the grain boundary or in the core depending on the magnetocrystalline anisotropy at the grain boundary defect layer. The texture dependency of the Grain Boundary Diffusion Process (GBDP) in sintered and hot-deformed Nd-Fe-B magnets was analyzed by creating a global and a local coercivity profile of the diffused samples. While the former method allows a conclusion on how the magnet acts as a whole, the latter allows a more precise resolution of local coercivity. In sintered magnets a slightly higher coercivity improvement was observed for the diffusion perpendicular to the texture axis. A pole hardening effect was observed for diffusion parallel to the texture axis that compensated the higher coercivity improvement for parallel diffusion. In hot deformed magnets on the other hand, no pole hardening effect was observed and a higher coercivity improvement was observed for parallel diffusion. A microstructural investigation showed that this effect could be attributed to the platelet shaped grains in hot deformed magnets. The in-situ demagnetization of hot-deformed magnets was analyzed for different Dy contents. The composition of different pilot batch Nd-Fe-B magnets by VACUUMSCHMELZE GmbH & Co. KG was determined by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES). The grain size distribution and orientation was determined using Electron Back Scattered Diffraction (EBSD). The influence of Heavy Rare Earth Elements (HRE) and microstructure engineering on the intrinsic and extrinsic magnetic properties was investigated. A similar minor loop investigation was also done for Nd-Fe-B sintered magnets showing that the vast majority of grains display a single domain like behavior despite being approximately one order of magnitude larger than the critical single domain size. Furthermore the amount of MDS during the demagnetization could be reduced by the addition of HRE