The challenge of addressing the discrepancy between intrinsic and extrinsic magnetic properties has been the focus of extensive research and development efforts. One subject of research is the development of new, unconventional processing techniques that enables the adjustment of a specific micro- or nanostructure. Severe plastic deformation (SPD) processes like high-pressure torsion (HPT) are well known for their potential to refine microstructures of a variety of metals and alloys. Yet, the method is not limited to the processing of monolithic samples but also capable of consolidating powders and powder blends. This enables the production of nanocomposite materials and microstructures that are inaccessible via conventional melting-based routes [1]. In this work, HPT is applied to powder blends consisting of hard magnetic SmCo₅ and different binder phases such as Cu and Sn. The ductile binder phase enables the plastic deformation of the compound and furthermore it decouples the hard magnetic SmCo₅ grains due to its nonmagnetic behavior. Microstructural analyses show a refinement of the brittle SmCo₅ phase initially by fragmentation via cracking which turns into plastic deformation at higher strains resulting in particle sizes in the single domain region. At very high shear strains (γ≈300), regions with nanocrystalline SmCo₅ embedded in an amorphous matrix are observed via transmission electron microscopy [2]. The individual particles are well surrounded by Cu leading to magnetic decoupling of the SmCo₅ grains and together with the grain refinement to an increase of the coercivity up to more than 1.3 T [3]. Furthermore, a crystallographic texture with the c-axis being preferably aligned parallel to the rotation axis of the HPT disc evolves, thus, leading to anisotropic magnetic properties. The results emphasize the wide freedom of microstructural design for magnetic materials using HPT of powder blends, which enables the generation of textured nanocomposites with excellent magnetic properties.

Acknowledgments

This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 405553726 – TRR 270, projects A08, A01, B04, Z01, Z02

References

[1] L. Weissitsch, F. Staab, K. Durst, A. Bachmaier, Magnetic Materials via High-Pressure Torsion of Powders, Mater. Trans. 64 (2023) 1537–1550.

[2] F. Staab, Y. Yang, E. Foya, E. Bruder, B. Zingsem, E. Adabifiroozjaei, D. Nasiou et al., Influence of amorphous phase on coercivity in SmCo5-Cu nanocomposites, Scr. Mater. 240 (2024) 115808.

[3] F. Staab, E. Bruder, L. Schäfer, K. Skokov, D. Koch, B. Zingsem, E. Adabifiroozjaei et al., Hard magnetic SmCo5-Cu nanocomposites produced by severe plastic deformation, Acta Mater. 246 (2023) 118709.