Thomas Kresse

Fe-based amorphous soft magnets have long been investigated with respect to alloy design and processing strategies to enhance saturation polarization (J_s) while preserving the amorphous phase essential for excellent soft magnetic properties and superior performance. This study demonstrates that Fe80B13Si7 melt-spun ribbons, containing a moderately high ferromagnetic fraction (~80 at%), display excellent amorphous stability, impressive soft magnetic behavior, and extremely low energy losses when processed under a highly efficient quenching atmosphere provided by helium. With the identical processing parameters, soft magnetic ribbons produced in helium gas provide a fully amorphous structure, whereas the ribbons synthesized in nitrogen undergo partial crystallization. The helium-quenched samples exhibit an exceptionally low mean coercivity (H_c) of ~1.3 A/m, in contrast to the nitrogen-quenched ones (mean H_c~14 A/m). The attained maximum permeability (μ_max) in helium (28.4 ± 1.3 (×10³)) is even comparable with commercial Metglas 2605SA1 (33.3 ± 4.8 (×10³)). The average saturation polarization (J_s) of the ribbons fabricated in both helium (~1.63 T) and nitrogen (~1.61 T) gases exceeds the commercial reference (~1.55 T). The helium environment showcases an excellent surface profile relative to nitrogen-induced quenching, which even shows a lower arithmetic mean surface height (S_a) than the reference material. Furthermore, the optimum annealing window for minimizing coercivity is found to lie approximately 15 to 20 K below the Curie temperatures (T_c) of the respective specimens. Core loss (P_core) measurements reveal substantial loss reduction in helium-quenched ribbons relative to nitrogen-quenched ones and even slightly lower than Metglas 2605SA1 at a lower polarization level (J~0.5 T). Therefore, this work establishes a comprehensive understanding of how helium and nitrogen gases, as quenching environments, influence the amorphous formation, magnetic softness, surface morphology, and energy losses of an alloy with a relatively high Fe content from the Fe-B-Si family to harness the material’s maximum potential.

Time-dependent magnetization losses critically affect the performance of permanent magnets during their service lifetime. Quantifying these losses remains challenging, as existing analytical models and simulation tools lack suitable functions for accurate prediction. This work introduces a practical method to quantify these losses using the magnetic viscosity parameter and to predict future behavior via the time-dependent fluctuation field. Measurements on several magnet grades demonstrate that long-term stability can be reliably estimated with this approach, supporting both analytical evaluation and direct implementation in numerical simulations. Validation against long-term experiments confirms the accuracy of the method and its suitability for predicting magnetization evolution, enabling more targeted material selection.

A new measurement method is presented for determining the magnetic viscosity parameter ( ${S}_{v}$ ) of permanent magnets (PMs) in various sizes and grades. $S_{v}$ , which describes the long-term stability of magnetic materials during operation, is measured using a setup with a magnetic yoke made of electrical steel enabling fast field changes. The measuring routine involves a sequence of small and large field pulses to determine direct and time-dependent losses, forming the basis for $S_{v}$ . Each measurement across several field stages is completed within 1 h, without the special sample preparation required by vibrating sample magnetometry (VSM) measurements. The effectiveness of this approach is confirmed by strong agreement with VSM measurements performed on different magnet types and at different temperatures.

Soft magnetic Fe-Al alloys have been a subject of research in the past. However, they never saw the same reception in technical applications as the Fe-Si or Fe-Ni alloys, which is, to some extent, due to a low ductility level and difficulties in manufacturing. Additive manufacturing (AM) technology could be a way to avoid issues in conventional manufacturing and produce soft magnetic components from these alloys, as has already been shown with similarly brittle Fe-Si alloys. While AM has already been applied to certain Fe-Al alloys, no magnetic properties of AM Fe-Al alloys have been reported in the literature so far. Therefore, in this work, a Fe-12Al alloy was additively manufactured through laser powder bed fusion (L-PBF) and characterized regarding its microstructure and magnetic properties. A comparison was made with the materials produced by casting and rolling, prepared from melts with an identical chemical composition. In order to improve the magnetic properties, a heat treatment at a higher temperature (1300 °C) than typically applied for conventionally manufactured materials (850–1150 °C) is proposed for the AM material. The specially heat-treated AM material reached values (H_C: 11.3 A/m; µ_max: 13.1 × 10³) that were close to the heat-treated cast material (H_C: 12.4 A/m; µ_max: 20.3 × 10³). While the DC magnetic values of hot- and cold-rolled materials (H_C: 3.2 to 4.1 A/m; µ_max: 36.6 to 40.4 × 10³) were not met, the AM material actually showed fewer losses than the rolled material under AC conditions. One explanation for this effect can be domain refinement effects. This study shows that it is possible to additively manufacture Fe-Al alloys with good soft magnetic behavior. With optimized manufacturing and post-processing, further improvements of the magnetic properties of AM L-PBF Fe-12Al may still be possible.

Laser powder bed fusion (L-PBF) was used to produce stator half-shells of a transverse flux machine from pure iron (99.9% Fe). In order to reduce iron losses in the bulk components, radially extending slits with a nominal width of 150 and 300 µm, respectively, were integrated during manufacturing. The components were subjected to a suitable heat treatment. In addition to a microscopic examination of the slit quality, the iron losses were also measured using both a commercial and a self-developed measurement setup. The investigations showed the iron losses can be reduced by up to 49% due to the integrated slits and the heat treatment.

Ferritic steel has the potential to act as a medium for magnetic storage of certain information, for example, to document the history of parts. The material is expected to play a role in supporting intelligent production processes and logistics routines for industrial internet applications. For writing and reading stable magnetic codes into steel, it is necessary to investigate and understand the corresponding requirements of the material. Both sensitively depend on characteristic microstructural details and related magnetic properties. They are either already present in the material or may be locally achieved in the code area by supplementary hardening methods.