Coercivity and its thermal stability of Nd Fe B hot-deformed magnets enhanced by the eutectic grain boundary diffusion process

Li, J.; Liu, Lihua; Sepehri-Amin, H.; Tang, Xin; Ohkubo, T.; Sakuma, Noritsugu; Shoji, Tetsuya; Kato, Akira; Schrefl, T.; Hono, K.

doi:10.1016/j.actamat.2018.09.018

Cited by 107 publications

(30 citation statements)

References 36 publications

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“…The difference in stability mainly depended on the Tb element distribution, phase structure, and grain boundary morphology at each diffusion depth [17,18]. The diffusion of Tb led to the grain exchange decoupling and high-Ha shell formation, which resulted in the increase of α and decrease in the number of magnetic atoms per unit volume (Neff) [8]. Therefore the sample kept a higher thermal stability.…”

Section: Resultsmentioning

confidence: 99%

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Nd-Fe-B Magnets: The Gradient Change of Microstructures and the Diffusion Principle after Grain Boundary Diffusion Process

Zhong

Yang

et al. 2019

Materials

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The diffusion of Tb in sintered Nd-Fe-B magnets by the grain boundary diffusion process can significantly enhance coercivity. However, due to the influence of microstructures at different depths, the coercivity increment and temperature stability gradually decreases with the increase of diffusion depth, and exhibit good corrosion resistance at a sub-surface layer (300–1000 μm). According to the Electron Probe Micro-analyzer (EPMA) test results and the diffusion mechanism, the grain boundary and intragranular diffusion behavior under different Tb concentration gradients were analyzed, and the diffusion was divided into three stages. The first stage is located on the surface of the magnet, which formed a thick core-shell structure and a large number of RE-rich phases. The second stage is located in the sub-surface layer, forming a uniform and continuous RE-rich phase and thin core-shell structure. The third stage is located deeper in the magnet, and the Tb enrichment only existed at the triangular grain boundary.

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Section: Resultsmentioning

confidence: 99%

“…GBDP is an important method to repair microstructures and improve coercivity by using HRE on the surface of the magnet to diffuse along the grain boundaries [7,8]. Marko et al [9] diffused TbF 3 powders through the grain boundaries, forming a uniform core-shell structure and increasing the coercivity by 50%.…”

Section: Introductionmentioning

confidence: 99%

Nd-Fe-B Magnets: The Gradient Change of Microstructures and the Diffusion Principle after Grain Boundary Diffusion Process

Zhong

Yang

et al. 2019

Materials

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“…This method is an extension of the Nd-Cu eutectic diffusion process that was invented to enhance the coercivity of HDDR powder [59] as well as hot-deformed magnets [60] without using HRE. High H c value of 2.3 T or 2.5 T was reported after the diffusion with Nd 70 Cu 30 [60] [58], Nd 62 Dy 20 Al 18 [62] and Nd 60 Tb 20 Cu 20 [63], the coercivity was further enhance to 2.6 -2.8 T at a processing temperature ≤ 700°C accompanied by a loss of remanence. This loss of remanence is more serious compared to the conventional HRE GBD process applied to sintered magnets, which is attribute to the formation of thick Nd-rich non-ferromagnetic intergranular phases observed in the eutectic diffusion processed hot-deformed magnets.…”

Section: How To Increase the Coercivity Of Hot-deformed Magnets Using Hre Diffusion Bypassing Grain Coarsening?mentioning

confidence: 98%

Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets

Sepehri-Amin

Sasaki

et al. 2021

Science and Technology of Advanced Materials

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Physically, the coercivity of permanent magnets should scale with the anisotropy field of ferromagnetic compounds, H A ; however, the typical coercivity values of commercial polycrystalline sintered magnets are only ~0.2H A , which is known as Brown's paradox. Recent advances in multi-scale microstructure characterizations using focused ion beam scanning electron microscope (FIB/SEM), aberration corrected scanning transmission electron microscopy (C s -corrected STEM), and atom probe tomography (APT) revealed detailed microstructural features of commercial and experimental Nd-Fe-B magnets. These investigations suggest the magnetism of a thin layer formed along grain boundaries (intergranular phase) is a critical factor that influence the coercivity of polycrystalline magnets. To determine the magnetism of the thin intergranular phase, soft X-ray magnetic circular dichroism (XMCD) and electron holography played critical role. Large scale micromagnetic simulations using the models that are close to real microstructure incorporating the recent microstructure characterization results gave insights on how the coercivity and its thermal stability is influenced by the microstructures.Based on these new findings, coercivity of Nd-Fe-B magnets are being improved to its limit. This review replies to most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets based on our recent studies.

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“…(3) Application of grain boundary engineering techniques such as the GBD process to hot-deformed magnets for a remarkable increase in coercivity with small HREE addition [36][37][38];…”

Section: Conclusion and Future Developmentmentioning

confidence: 99%

High performance hot-deformed Nd-Fe-B magnets (Review)

Hioki

2021

Science and Technology of Advanced Materials

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Coercivity and its thermal stability of Nd Fe B hot-deformed magnets enhanced by the eutectic grain boundary diffusion process

Cited by 107 publications

References 36 publications

Nd-Fe-B Magnets: The Gradient Change of Microstructures and the Diffusion Principle after Grain Boundary Diffusion Process

Nd-Fe-B Magnets: The Gradient Change of Microstructures and the Diffusion Principle after Grain Boundary Diffusion Process

Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets

High performance hot-deformed Nd-Fe-B magnets (Review)

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