Understanding the microstructure and coercivity of high performance NdFeB-based magnets

Woodcock, T.G.; Zhang, Yuepeng; Hrkac, G.; Ciuta, Georgeta; Dempsey, Nora; Schrefl, T.; Gutfleisch, Oliver; Givord, D.

doi:10.1016/j.scriptamat.2012.05.038

Cited by 206 publications

(81 citation statements)

References 31 publications

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“…Consequently, the static magnetic coupling and the domain wall pinning effect between the main phase grains of the two-stage aged samples are weakened. Hence, the magnetic properties, i.e., the intrinsic coercive force of the magnets is improved [14]. This finding agrees well with the theory proposed by Vial et al [15], which indicates that the microstructures of the sintered Dy-doped NdFeB magnets after the two-stage aging treatment will be more uniform and the magnetic properties will significantly increase, especially the intrinsic coercivities.…”

Section: Fracture Mechanism Analysissupporting

confidence: 90%

Brittleness and fracture mechanism of sintered Dy-doped NdFeB magnets

et al. 2015

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The brittleness and fracture behaviors of the sintered and the two-stage aged Dy-doped NdFeB magnets were studied by a unique method of acoustic emission testing and Vickers hardness indentation method in this paper. A detailed analysis on the crack propagation mechanism along the grain boundary of the main grain phase (Nd, Dy) 2 Fe 14 B was done. By comparing the acoustic emission energy count value (E n ) with the Vickers hardness indentation load (P), it is shown that there is a linear relationship between E n and P for both the sintered and the two-stage aged Dy-doped NdFeB magnets. According to the slope of E n versus P linear lines, it can be found that the two-stage aged Dy-doped NdFeB magnet is more brittle than the sintered one. It is due to that the Ndrich grain boundary phase of the two-stage aged Dy-doped NdFeB magnet is formed as thin film and uniformly distributes around the main grain phase, which plays a significant role in increasing the intrinsic coercive force of the magnet, but decreasing its interface binding strength. Therefore, the resistance of crack propagation along the grain boundary decreases and the brittleness increases.

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Section: Fracture Mechanism Analysissupporting

confidence: 90%

Brittleness and fracture mechanism of sintered Dy-doped NdFeB magnets

et al. 2015

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“…Microstructures of the material have been studied to help understand the mechanism of oxidation [18,[61][62][63][64]. Outer scales or external oxidation zone (EOZ), identified as Fe 2 O 3 and Fe 3 O 4 by scanning electron microscopy (SEM), were found to form at 573-873 K and zones of internal oxidation were also observed, confirming that the principal degradation process is by inward diffusion of oxygen.…”

Section: Ndfeb's Oxidation Thermodynamics Kinetics and Mechanismmentioning

confidence: 99%

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

Firdaus

Rhamdhani

Durandet

et al. 2016

J. Sustain. Metall.

104

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Rare-earth metals, particularly neodymium, dysprosium, and praseodymium are becoming increasingly important in the transition to a green economy due to their essential role in permanent magnet applications such as in electric motors and generators. With the increasingly limited rare-earth supply and complexity of processing Nd, Dy, and Pr from primary ores, recycling of rare-earth based magnets has become a necessary option to manage supply and demand. Depending on the form of the starting material (sludge or scrap), there are different routes that can be used to recover neodymium from secondary sources, ranging from hydrometallurgical (based on its primary production process), electrochemical to pyrometallurgical. Pyrometallurgical routes provide solution in cases where water is scarce and generation of waste is to be limited. This paper presents a systematic review of previous studies on the high-temperature (pyrometallurgical) recovery of rare earths from magnets. The features and conditions at which the recycling processes had been studied are mapped and evaluated technically. The review also highlights the reaction mechanisms, behaviors of the rare-earth elements, and the formation of intermediate compounds in high-temperature recycling processes. Recommendations for further scientific research to enable the development of recovery of the rare-earth and magnet recycling are also presented.

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“…It can be seen that grains of Nd 2 Fe 14 B of both magnets are surrounded by Nd-rich phases which form thin, continuous and uniform layers along the Nd 2 Fe 14 B grain boundaries and form smaller grains at the Nd 2 Fe 14 B grain junctions. Therefore, the magnetic exchange interaction between the neighboring Nd 2 Fe 14 B grains can be removed so as to increase the intrinsic coercivity [3]. Compared to the low-temperature aged magnets, the grain size of the two-stage aged magnets is fine because of the recrystallization during high temperature ageing process.…”

Section: Magnetic Properties Detectionmentioning

confidence: 99%

“…Compared to conventional Nd-Fe-B magnets, the Dy-doped magnets are widely used because of their improved intrinsic coercivity [1−2], the Curie temperature [3] and the corrosion resistance [4]. The excellent magnetic property of the Dy-doped magnets is usually required by a two-stage ageing process which includes high-temperature ageing and low-temperature one.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and properties of low-temperature aged Dy-doped Nd-Fe-B magnet

Wang

Ding

et al. 2016

J. Cent. South Univ.

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In this work, a low temperature ageing process for the high coercivity Dy-doped Nd-Fe-B magnets was developed by the optimizing ageing process. The experimental results show that there is no difference in microstructures, crystal orientation, magnetic and mechanical properties between the low-temperature aged and the two-stage aged sintered Dy-doped Nd-Fe-B magnets. Because of the uneven stress distribution in the sintered Dy-doped Nd-Fe-B magnet and the high activation of Dy element, Dy atoms could diffuse into the main crystal phase and the grain boundary phases of the magnets during low-temperature ageing process, which results in the reasonable distribution of Dy element and formation of the thin and uniform grain boundary phases, which are the main reasons to improve intrinsic coercivity of the Dy-doped Nd-Fe-B magnets by the low-temperature ageing.

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Understanding the microstructure and coercivity of high performance NdFeB-based magnets

Cited by 206 publications

References 31 publications

Brittleness and fracture mechanism of sintered Dy-doped NdFeB magnets

Brittleness and fracture mechanism of sintered Dy-doped NdFeB magnets

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

Microstructure and properties of low-temperature aged Dy-doped Nd-Fe-B magnet

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