NdFeB permanent magnets are produced based on rare earths elements (REE). In addition to neodymium, praseodymium, dysprosium and terbium are also used to achieve the special magnetic properties. Due to the special physical properties of rare earth elements, sintered NdFeB permanent magnet materials achieve the highest energy densities today. Due to the tetragonal crystal structure of the Nd2Fe14B compound, a maximum energy density of 62MGOe can be achieved.
The application areas for NdFeB permanent magnet materials range from simple holding magnets to automotive applications and aerospace.
Due to the wide range of possible applications for NdFeB magnets, BEC has a wide range of material compositions. Targeted changes in the alloy composition allow the temperature and corrosion resistance, magnetic properties and other parameters of the magnet to be adapted to the customer’s specific requirements.
Typically, the application temperatures for NdFeB permanent magnets range from -40C to a maximum of +240°C.
When sintered NdFeB permanent magnets are compared with SmCo permanent magnets, two major differences to the disadvantage of NdFeB magnets become apparent. The low Curie temperature, which leads to high temperature coefficients of remanence and coercive field strength, are just as problematic as the high susceptibility to corrosion of the Nd rich phase in the microstructure.
Through our partnerships with suppliers, continuous development and research has gradually eliminated these deficits. Process optimization and adaptation of the microstructure within the crystalline structure contributed to this.
For this reason, BEC specifies and guarantees its customers the coercivity HcJ at maximum application temperature, usually at 150°C and not only at room temperature.
The temporary yet tense situation in the rare earth market, the increasing demand for dysprosium (Dy) and terbium (Tb) – which weaken, or even free NdFeB permanent magnets –, as well as the impressive progress in manufacturing processes have prompted BEC to focus its development activities on reducing the share of the heavy rare earth elements (HREE) Dy and Tb. The new permanent magnet materials are symbolically called TERRAMAG® Light. Their main characteristic is that they feature the same corrosion and temperature resistance as the TERRAMAG® of the S and H-N permanent magnet materials and at the same time reduce the dependence on possible bottlenecks in the SEE supply.
TERRAMAG® Z and “Zero” permanent magnet materials are free of Dy and Tb. Is important to keep in mind that Dy- and Tb-free permanent magnet materials which meet the temperature resistance criteria of TERRAMAG® materials with respect to HcJ at the maximum application temperature can only be produced up to a maximum of 150°C with the technologies available today. The TERRAMAG® ZS and ZH – N permanent magnet materials fully meet the BEC resistance criteria of S and H-N permanent magnet materials, respectively.
As mentioned, in the manufacture of NdFeB permanent magnets for application temperatures above, around, 150°C, Dy and / or Tb cannot be avoided. Our development activities have concentrated on reducing the Dy and Tb contents for these TERRAMAG® permanent magnet materials. The developed TERRAMAG® RS or RH-N materials, R as in “reduced”, achieve the same properties as the TERRAMAG® S or H-N permanent magnet materials through adapted processes with 2 – 4 wt.% less Dy- or Tb contents.
TERRAMAG® L – Series
Already in the 90s, through publications, it became known that very large grains in the sintered NdFeB permanent magnets can show a non-homogeneous Dy – distribution. Dy forms a kind of “shell” at the grain boundaries, which increases the coercivity HcJ considerably. Through the continuous R&D activities, not only in the field of material sciences, but also in the field of manufacturing processes, an additional series in the TERRAMAG® family was developed. The L – materials, L like “lean”, are produced by the Grain Boundary Diffusion Process (GBDP), a technology in which the heavy rare earths Dy and Tb are “incorporated” into the grain boundaries of the NdFeB permanent magnets by a diffusion process. For an effective diffusion, however, there are limitations in the magnet dimensions, so a maximum height of 10 mm must not be exceeded at present. The magnetic parameters of TERRAMAG® LS and LH-N permanent magnet materials are comparable to those of TERRAMAG® S and H-N materials.