LOEWE-Focus RESPONSE (Resource-saving Permanent Magnets by Optimized Use of Rare Earth) Subproject: New Synthesizing Process Top-Down
Modern high-performance permanent magnets represent a key component for the continuously growing electric mobility such as hybrid or electric drives. They are also important components in alternative energy generation methods such as wind power generators. To achieve a particularly high energy density, magnets are used with a large amount of rare earths, which have unique electronic, magnetic and optical properties. Compared to rare earth-based materials, classical magnetic materials have only one-fifth of the energy density. However, the extraction of rare earths is highly energy-intensive due to geological deposits as well as the chemical similarity and causes intense pollution of the environment. At the same time rare earths are subjected to big market dependencies.
The use of rare earths will increase with further development of alternative energy generation methods which include these high-performance permanent magnets.
This research project has two main objectives. On the one hand, the aim is to reduce or to substitute the proportion of rare earths in the strongest rare earth magnets without having significant performance losses. The use of these magnets will focus further on high performance application range in electric motors and generators for wind turbines. Second objective is to develop new magnets of the next generation without rare earths with much higher energy density than conventional magnetic materials. These magnets are expected to be used in small electric motors for medium to high temperature range.
In cooperation with the Fraunhofer Project Group and the Technical University of Darmstadt in the fields of materials science, chemistry, physics and engineering, methods for the achievement of the described project objectives are developed. The focus of the project “New methods of synthesis” is to develop a process chain that enables grain refining and continuous production of highly textured magnetically anisotropic samples. For grain refinement and induction of high defect densities in soft and hard magnetic materials, the continuous ECAS process (Equal Channel Angular Swaging) is intended to be used. This process will produce a nanocrystalline isotropic preform with high coercive field strength. A texture in the material is realized by a downstream rotary swaging process and/or by a magnetically enhanced heat treatment.
Within the RESPONSE project, changes in the microstructure could be proved by forming processes, as well as their correlation can be determined. In the case of the soft magnetic material Fe83Co17, the forming textures in the form of elongated grains can be observed after rotary swaging. This is responsible for the increased shape anisotropy. On the other side, the grain size of Fe83Co17 decreases due to the large shear stress generated by ECAS process. For this, a tool is designed for the ECAS process and manufactured on the high-speed press machine with a continuous feed device. The magnetic properties of Fe83Co17 samples are increased due to the both changes in the microstructure.
Further important findings are obtained from the rare earth-containing hard magnetic material Nd-Fe-B. This material is only soft magnetic in the as-cast state. After swaging the encapsulated samples at an increased temperature, a significant increase of hard magnetic properties is observed. The magnetic hardening is due to the grain refining in the material. The brittle grains of the 2-14-1 main phase break under stress and the grain boundary phase, which is liquid at process temperature, flows at the same time into the occurred cracks. Therefore, the grain refining can take place without rupturing the entire sample.
Parts of the current research in this field are funded by the German federal state of Hesse (project "LOEWE-Focus RESPONSE (Resource-saving Permanent Magnets by Optimized Use of Rare Earth“).
This financial support is gratefully acknowledged.