Speaker
Description
Soft magnetic materials formed by hot powder powder compaction are a distinct class with significant application potential. They possess exceptional magnetic properties, such as low core losses, high permeability, and $3$-D isotropic magnetic behavior. The shape and size distribution of the powder particles, along with the processing conditions such as compaction temperature and pressure, determine the final density, mechanical, and magnetic properties of the compacted soft magnetic material. Furthermore, the shape of the particles and the level of porosity in compacted materials significantly impact their magnetic behavior. The surfaces of the ferromagnetic particles within the porous structure of powder compacts create internal demagnetizing fields, which negatively impact the magnetic permeability. These demagnetizing fields diminish the internal magnetic field within the compacted material, leading to a reduction in its permeability. Rough surfaces also hinder the movement of domain walls in ferromagnetic materials.
In this study, two ring-shaped specimens were prepared by hot powder compaction. Resulting specimen had outer and inner diameters of $24$ mm and $18$ mm, respectively, with a height of $3$ mm. The compaction was performed at a pressure of $700$ MPa for $3$ minutes at a temperature of $400$ °C. The powder used in compaction was prepared by: (i) grinding pure iron granulates in a planetary ball mill, (ii) extracting a size fraction of $63-125$ $\mu$m by sieving, and (iii) annealing for $90$ minutes at $400$ °C. The first ring-shaped sample was prepared using the initial powder, while the second sample was prepared with powder that underwent an additional surface smoothing treatment using grinding paper with SiC grit of grade P$1200$. Microstructure of the compacted materials was examined using X-ray absorption tomography with a Zeiss XRadia $610$ Versa. The variation in the atomic structure of compacted materials was analyzed by conducting a line scan in transmission geometry across the sample width using a well-focused ( $9\;\mu$m $\times 2\;\mu$m) high-energy ($67.8$ keV) photon beam at the P$21.2$ synchrotron beamline at PETRA III in DESY, Hamburg, Germany.
Acknowledgements
This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III and we would like to thank U. Linenert for assistance in using P21.2 beamline.
