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5. Funktionswerkstoffe und Werkstoffverbunde für die Energiewende

Author

Leich, Lennart (M. Sc.)

Subjects
Widerstandspressschweißen, Kupfer, Sintern, ddc:620, Gefüge (Werkstoffkunde), Wolfram
Abstract

Das Ziel dieser Arbeit war die Gewinnung grundlegender Erkenntnisse zur energieeffizienten Herstellung von Funktionswerkstoffen und Werkstoffverbunden für die Energiewende sowie die Betrachtung der entstehenden Gefüge und der damit verbundenen Eigenschaften. Zur Urformung metallischer Pulverpartikel wurde auf das Kondensatorentladungssintern (EDS, engl. Electric-Discharge Sintering) zurückgegriffen und zum Fügen von Werkstoffverbunden fand das Widerstandspressschweißen an einer modernen Schweißanlage Anwendung. Als Werkstoffe wurden neben Magnetwerkstoffen des Systems Neodym-Eisen-Bor (NdFeB) und Verbund-Kontaktwerkstoffen der Systeme Kupfer-Wolfram (CuW), Kupfer-Chrom (CuCr) und Silberzinnoxid (AgSnO2) auch hochleitfähige Werkstoffverbunde aus Aluminium und Kupfer betrachtet.

Published
2022

7. NdFeB Magnets with Well‐Pronounced Anisotropic Magnetic Properties Made by Electric Current‐Assisted Sintering.

Author

Prasad Mishra, Tarini, Leich, Lennart, Krengel, Martin, Weber, Sebastian, Röttger, Arne, and Bram, Martin

Subjects
MAGNETIC properties, ELECTRIC properties, SINTERING, MAGNETS, SUPERCONDUCTING magnets, WASTE products, POWDERS, PARTICLE size distribution
Abstract

Electric current‐assisted sintering (ECAS) technologies are highly promising for processing of NdFeB magnets. Due to the combination of direct Joule heating and application of external load, even powders, whose particle size distribution and morphology are not optimum for conventional powder processing like melt‐spun powders or magnet scrap, can be easily sintered to high densities. A systematic study is done to demonstrate the potential of field‐assisted sintering technique/spark plasma sintering (FAST/SPS) and flash spark plasma sintering (flash SPS) for sintering of NdFeB powders. Melt‐spun, commercial NdFeB powder (Magnequench MQU‐F) is used as starting material. Its platelet‐like shape makes this powder extremely difficult to sinter by conventional methods. This study clearly reveals that especially in the case of flash SPS application of external pressure in combination with short cycle times enables to achieve well‐pronounced anisotropic magnetic properties without the need of subsequent upset forging. Optimized flash SPS parameters are applied to NdFeB magnet scrap with broad particle size distribution, demonstrating the general potential of ECAS technologies for recycling of waste magnet materials. Finally, the results are benchmarked with respect to established NdFeB processing technologies and electrodischarge sintering (EDS), another promising ECAS technology with very short cycling time. [ABSTRACT FROM AUTHOR]

Published
2023
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8. Electro-discharge sintering of nanocrystalline NdFeB magnets

Author

Leich, Lennart (Dr.-Ing.), Röttger, Arne (Prof. Dr.-Ing.), Kuchenbecker, Rene, and Theisen, Werner (Prof. Dr.-Ing.)

Subjects
ddc:620
Abstract

This study investigates the compaction of nanocrystalline NdFeB magnet powder by electro-discharge sintering (EDS). On this account, process parameters, microstructure, and the associated magnetic properties of the EDS-densified nanocrystalline NdFeB specimens were investigated by varying the discharge energy \(E_{EDS}\) and compression load \(\it {p}_{EDS}\). Although optimized process parameters could be evaluated, three different microstructures (fully densified zone, insufficiently densified zone, and melted zone) are present in the EDS-compacted specimens. Thereby, volume fractions of these formed three different microstructures determine the resulting mechanical and magnetic properties of the specimens. For all specimens, the intrinsic coercivity \(H_{c,J}\) deteriorates with increasing discharge energy, as the generated Joule heat leads to microstructural changes (grain growth, dissolution of magnetic phases), which reduces the magnetic properties. The compression load has less influence on the coercivity \(H_{c,J}\), as it only affects the initial resistance of the pre-compacted powder loose. The residual induction \(B_{r}\) deteriorates with increasing the discharge energy due to microstructural changes. An increase in the compression load \(\it {p}_{EDS}\) results in an increase in the specimens' density and thus promotes the residual induction \(B_{r}\).

Published
2020

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