13th International Conference on Advanced Materials and Nanotechnology
Jožef Stefan Institute, Slovenia
Title: Towards Minimizing the Consumption of Heavy Rare Earths in the Processing Of Nd-Fe-B Permanent Magnets by Electrophoretic Deposition
Biography: Marko Soderžnik
With their high performance, Nd-Fe-B sintered permanent magnets are the most promising candidates for a variety of transportation application. Heavy rare earths (HRE), such as Dy or Tb are inevitably used in Nd-Fe-B permanent magnets that exhibit high magnetic performance at elevated temperatures. Particularly, high coercivity of the magnets is important to oppose high demagnetization fields, caused in the electromotor. Drastic reduction of Dy- or Tb-consumption was achieved by using the grain-boundary diffusion process initiated by the electrophoretic deposition of nano TbF3 particles. At the same time, the magnetic properties remained unaffected. Commercially available Nd-Fe-B magnets were coated by EPD with nano TbF3. Scanning electron microscopy revealed uniform layer of nano TbF3 which was well attached to the surface of the magnet. Good adhesion of powder is one of the main quality parameters for the successful grain-boundary diffusion process. Compared to simple dip-coating, EPD gives better adhesion of TbF3 powder and consequently higher coercivity after the GBDP. The coercivity achieved after the EPD-based GBDP was 1536 kA/m at 75 °C, which is nearly twice that of the uncoated sintered magnet and 1.5 times higher than that for the uncoated magnet exposed to the same heat treatment. To measure the accurate amounts of the elements, especially Tb, the chemical composition was determined with induction coupled plasma optical electron spectroscopy (ICP-OES). The microstructural investigation was done with a high resolution field emission SEM. Core-shell-type microstructure was formed after the processing.