Skip to Main content Skip to Navigation
Theses

Coercivity of NdFeB-based sintered permanent magnets : experimental and numerical approaches

Abstract : Nd-Fe-B permanent magnets are the most powerful among all commercially available magnets. They play a significant role in energy applications, such as motors of electric vehicles and generators of windmills. Their outstanding properties come from the excellent intrinsic magnetic properties of the Nd2Fe14B phase and from their microstructure. However, electrical machines operate at about 120-180°C and extrinsic magnetic properties such as coercivity and remanence decrease rapidly with temperature. One way of improving coercivity of Nd-Fe-B sintered magnets is to substitute Nd with a heavy rare earth such as Dy, so as to increase the magnetocrystalline anisotropy. However, Dy is a strategic element and a major objective of the research community is therefore to develop Nd-Fe-B magnets that possess excellent extrinsic magnetic properties with a reduced content of Dy. This requires a better understanding of the link between microstructure and coercivity. The key point is the control of the grain size and the distribution of secondary phases at grain boundaries to prevent magnetization reversal and magnetic coupling. The first part of this thesis concerns a comparison of open-circuit and closed-circuit magnetization measurements carried out on Nd-Fe-B sintered magnets. The observed differences in coercivity values are discussed in terms of magnetic viscosity and demagnetizing field effects. The second part deals with the grain boundary diffusion process performed on Nd-Fe-B sintered magnets using Dy-Co alloys. Microstructural observations and magnetic measurements have been carried out to characterize the diffusion and coercivity profiles and to establish the link between local variations in composition and coercivity. Moreover, micromagnetic simulations have been performed to describe magnetization reversal at the nanoscale in a simple core-shell model. The last part constitutes a discussion about coercivity in graded magnets via a diffusion model and further simulations on a polycrystalline model.
Complete list of metadatas

Cited literature [153 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-02635105
Contributor : Abes Star :  Contact
Submitted on : Wednesday, May 27, 2020 - 5:12:06 PM
Last modification on : Tuesday, October 20, 2020 - 10:46:48 AM

File

FLIEGANS_2019_archivage.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02635105, version 1

Collections

Citation

Jérôme Fliegans. Coercivity of NdFeB-based sintered permanent magnets : experimental and numerical approaches. Materials Science [cond-mat.mtrl-sci]. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAY071⟩. ⟨tel-02635105⟩

Share

Metrics

Record views

76

Files downloads

148