Projects / Programmes source: ARIS

High-coercivity Nd-Fe-B permanent magnets with minimum amount of heavy rare earths

Research activity

Code Science Field Subfield
2.04.00  Engineering sciences and technologies  Materials science and technology   

Code Science Field
T150  Technological sciences  Material technology 

Code Science Field
2.05  Engineering and Technology  Materials engineering 
Nd-Fe-B permanet magnets, high-coercivity magnets, grain-boundary diffusion process, electrophoretic deposition, reduction of heavy rare earths
Evaluation (rules)
source: COBISS
Researchers (1)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  32166  PhD Marko Soderžnik  Materials science and technology  Head  2016 - 2017  111 
Organisations (1)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,921 
Abstract Nd-Fe-B permanent magnets play an important role in rapidly-growing alternative-energy devices (electric vehicles, hybrid-electric vehicles and wind turbines). Such devices are able to exploit the largest maximum energy product (BHmax) among all other magnets. Unfortunately, there is still a room for improvement the coercivity, since magnets based on the Nd2Fe14B hard-magnetic phase have a theoretical maximum coercivity in excess of 6000 kA/m. What limits Nd2Fe14B-based magnets without Dy and Tb (HRE) to 1500 kA/m is their microstructure. One of the options for adding Dy or Tb into the Nd2Fe14B matrix phase is the blending technique. In this case usually 2 wt. % to 10 wt. % of Dy or Tb is added to improve the coercivity. These two crucial elements became extremely expensive and they couple antiferomagnetically with Fe in the tetragonal crystal structure, which causes a large negative effect on the remanence. Within this project, their amount in magnets will be drastically reduced. However, the coercivity will be significantly improved, while the remanence will stay almost unchanged. The proposed research project “High-coercivity Nd-Fe-B permanent magnets with minimum amount of heavy rare earths“ focuses on the post-sintering process, which enables us to reduce the amount of critical heavy rare earth (HRE) elements in the Nd-Fe-B magnet and at the same time retain the magnetic properties at a high level. Such a process can reduce the final price of the magnet, since it spends lower quantity of expensive Dy or Tb (HRE) and the magnet is then able to operate at elevated temperatures (100 °C) without sacrificing its efficiency. The main objectives of the proposed project are systematic optimization of all the suspension and also the process parameters. Those parameters are crucial for achieving the first goal, the successful electrophoretic deposition (EPD) of TbF3 powder on the surface of sintered Nd‑Fe‑B permanent magnets. Such EPD-coated magnets will be exposed to different heat-treatment-regimes at elevated temperatures, when the so called grain-boundary diffusion process (GBDP) will occur. The consequence of such GBDP will be significantly higher coercivity. To characterize the improved magnets, various analytical techniques will be used. The magnetic measurements at different temperatures will be done with permeameter and vibrating-sample magnetometer (VSM). On the other hand, microstructural observations and chemical analyses will be performed by means of field-emission-gun scanning electron microscope (FEG-SEM) and high resolution transmission electron microscope (HRTEM). Analyses on the atomic, high-resolution (HR) level allow immediate insight into the chemistry and structure of the sample, without modelling simulations. The aim is to reveal the microstructural features which lead into the improved magnetic properties. α (coercivity dependence) and β (remanence dependence) temperature coefficients will be calculated from the hysteresis loops. From the microstructural data, the calculations will be done to figure out how high is the Tb-concentration after the GBDP or two-step GBDP. With the EPD I will be able to deposit an exactly known amount of TbF3-powder on the surface. This is very important for industrial applications, where the costs of heavy rare-earths are a critical factor. The improved magnets could be potentially interesting for the transfer into the industrial production lines.
Significance for science
The basic goal of the project was to continue and upgrade my current research work in the field of sintered NdFeB magnets for the application in electric/hybrid cars and wind turbines, which are of essential environmental importance. The purpose of the research project was the systematic and efficient implementation of all optimization and processing stages in the EPD of TbF3. Moreover, the GBDP had to assure the highest degree of diffusion, which allowed the maximum coercivity with minimum reduction in remanence. Nevertheless, the correlation between the magnetic properties and the microstructural characterization is one of the crucial understandings of the nucleationtype coercivity mechanism. The important relevance to the development of scientific field were diverse: -Understanding and describtion of the EPD based GBDP of TbF3 powder, which drastically enhanced the coercivity; Technology knowhow. -The repeatability of the “process and magnetic measurements” were ensured with the optimization. -I achieved the best coercivity with the highest magnetocrytalline anisotropy Tb2Fe14B phase and minimum addition of TbF3 powder, which has a tremendous importance for the further development. The dissemination activities that contribute to the development of science and scientific field: -Publications of the articles in international scientific journals with high impact factor. -Publications of the individual chapters in international scientific monographs. -Invited lectures at conferences, workshops and symposia. -International involvement and collaboration with research institutions around the world. -Networking within the collaboration with different research institutes worldwide. -Disseminating knowledge among younger generations, since I am a working mentor to a postdoctoral student and to many young stundents who work in our department.
Significance for the country
Direct impact of a specially engineered magnet with low amount of HRE and at the same time high coercivity is in applicability and usefulness. As mentioned before, the highcoer civity magnets are widely used in rapidly growing alternative energy devices (electric vehicles, hybridelectric vehicles and wind turbines). Because of the need in the conventional processing of Nd-Fe-B magnets to have a lot of rare earth rich grain boundary phase, the starting alloy normally contains about 2–10 wt % of HRE. By removing the need for this 2–10 wt % of HRE this technology can, in the long term, free the European manufacturers from a dependence on restricted supplies of strategic elements (Dy and Tb) from China. It is important to understand the phrase “drastic reduction of Tb content” in the proposal in the context of permanent magnets; reducing the HRE amounts as described in the proposal, ed to a drastic reduction of Tb content. Within the project I applied the original idea of EPD, to effectively use the TbF , and greatly reduce the quantities of Tb, which is on the top of the list of Critical Raw Materials published by the European Commission in 2014 (detailed explanation is in the description of the work program). On the European level, many Nd-Fe-B related companies are located in Slovenia. There will be a great possibility for the cooperation with those companies (Magneti Ljubljana, LetrikaMahle Šempeter pri Novi Gorici, Kolektor Idrija, Bosch…).
Most important scientific results Final report
Most important socioeconomically and culturally relevant results Final report
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