Within the framework of the ARIS Z2-2645 project (https://www.ijs.si/ijsw/ARRSProjekti/2020/Z2-2645) we developed strategies for rapid consolidation of Nd-Fe-B-type magnets based on a novel approach of intense thermal radiation, i.e., Radiation-Assisted Sintering (RAS). Rapid densification and sintering occur in a modified conventional Spark Plasma Sintering (SPS) furnace, enabling fast and efficient heating. The novel furnace arrangement allows no pressure to be applied to the magnetically oriented green compacts. The latter is of decisive importance in preserving the pre-aligned magnetic texture in the final magnet, which leads to higher remanent magnetization values (Br) and high energy products (BH)max, with comparable coercivities (Hci) to conventional sintering. The new RAS strategy enables the densification of standard Nd-Fe-B powders in just 10 minutes, with magnetic properties comparable to magnets prepared in a conventional way. It is important to emphasize that short heating cycles reduce the energy consumption required to prepare advanced Nd-Fe-B magnets by an order of magnitude compared to slow, hours-long, conventional sintering strategies.
In 2023, we finished the project in the scheme EIT RAW Materials 21043 RECO2MAG (https://reco2mag.rgf.bg.ac.rs/), whose primary aim was to assist the industry in developing Nd-Fe-B permanent magnets with improved properties. We have developed innovative methods that include improved jet-milling of strip-cast Nd-Fe-B feedstocks. With further additions of NdH3 and DyF3, we have raised the magnetic properties denoted as magnetic grades from the current N38M to N48M (Br=1.2T→1.4T). At the same time, we also increased the coercivity from class M to UH (1200 kA/m (M)→1800 kA/m (UH)). We also successfully implemented the electrophoretic deposition of heavy rare earths to industrially produced Nd-Fe-B magnets. With the subsequent process of diffusion of heavy rare earths along the grain boundaries, we achieved an increase in coercivity from M grade to SH grade (1100 kA/m (M) to 1750 kA/m (SH)).
We continued our research within the EIT RAW Materials INSPIRES project (https://inspires-magnet.eu/). The project focuses on recycling and reprocessing of Nd-Fe-B permanent magnets. We conducted jet-milling of Hydrogen-Processed Magnetic Scrap (HPMS) received from Pforzheim University, followed by sintering trials incorporating DyF3 and NdH3 additives for enhanced coercivity. Both conventional and rapid sintering methods were employed with RAS showing a 30% increase in coercivity to ~1300 kA/m compared to conventional methods. Using the HPMS process we successfully recycled 10 kg of waste magnets. We produced powders suitable for sensor applications with coercive force Hci = 600 kA/m and remanent magnetization Br = 0.75 T to be further processed into bonded magnets at industrial partner Kolektor KFH.
