Colloquia Series on Sustainable Metallurgy: Tailorable and rare-earth free magnetic materials by severe plastic deformation

Severe plastic deformation is a well-established method for producing nanocrystalline and ultrafine-grained materials. Among severe plastic deformation techniques, high-pressure torsion (HPT) is particularly versatile. In addition to deforming bulk materials, HPT can be used for mixing, consolidation, and alloying of powders at ambient temperatures through high shear strain. This avoids high-temperature processing steps, such as sintering, which can lead to decomposition, and bypasses the limitations imposed by phase diagrams and traditional metallurgical routes. While HPT has traditionally been used to tailor and study advanced mechanical properties, recent interest has increasingly shifted toward functional properties.In this talk, the use of HPT deformation to synthesize different magnetic materials is in focus. Magnetic properties are strongly governed by microstructure. By selecting different starting materials and controlling grain size, phase distribution and texture formation, HPT provides powerful opportunities to tune magnetic properties. In HPT deformed binary and ternary immiscible systems, soft magnetic properties are obtained. Additionally, the use of the HPT deformation process to synthesize hard magnetic materials and nanocomposites entitling different magnetic coupling mechanisms as well as exchange biased ferro- antiferromagnetic magnets is presented.The research on rare-earth free magnetic materials has increased significantly in recent years, driven by criticality of the strategic rare earth elements. The ferromagnetic α-MnBi phase as rare-earth free magnetic material has gained increasing interest, but the fabrication of large volumes containing a significant amount of α-MnBi is still challenging. Finally, I will address the use of HPT deformation to synthesize the rare-earth free α-MnBi phase from elemental Mn and Bi powders avoiding a large number of different processing steps. Speaker: Prof. Andrea Bachmaier

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