Spomenka Kobe

Abstract:

Permanent magnets are vital components in the rapidly-developing renewable energy sector, where the motors for electric vehicles and the generators in wind turbines require strong magnets with the ability to operate at temperatures well over 100°C. To achieve high coercivity, remanence and consequently high energy product at elevated temperatures, the addition of heavy rare earth (HRE) to the basic Nd-Fe-B composition is needed. To minimize the amount of critical elements such as dysprosium or terbium, the grain boundary diffusion process is applied on sintered magnets. Instead of using dipping in slurry of HRE or expensive sputtering, a new chemical process was invented – electrophoretic deposition (EPD). EPD-modified GBDP showed much better coercivities after an optimum heat treatment; it was shown that the coercivity can be also tailored; it depends on the DyF3 powder thickness on the magnet before heat treatment. From our results, it is apparent that the EPD process has two advantages: extra materials costs associated with the heavy-rare-earth component of the magnets can be minimised and a reduction of the environmental impact because we are not wasting any heavy rare earth during the procedure. By this new method, we could minimize the amount of HRE used to 0.2 at %. The improvement of coercivity was 30 % with minimal loss in remanence. To study the mechanism for such an improvement in coercivity without significantly decreasing the remanence, a detailed microstructure investigation was performed. The technology was transferred to the industrial partner on a pilot production level and the final products will be used in the demonstrating motors for electric car and a wind turbine. Acknowledgment: FP7-NMP-2012-SMALL-6 Contract No.: 309729