Sustainable electric propulsion systems require sophisticated combination of pole design and magnetic materials to provide the needed torque at a wide range of rotational speeds. One possible way to meet this challenge is the application of tailored magnetic materials. Magnetic composites often act as functional materials with properties tailored to their applications. With microstructural modification, properties like coercivity (Hc), remanence (Br), saturation magnetization (Ms) and maximum energy product (BHmax) can be optimized.
In this thesis, the feasibility of magnetic composite fabrication by high-pressure torsion (HPT) is studied. Magnetic composites are fabricated using the multi-sector disk approach for bulk materials. In addition, the magnetic composites are fabricated by powder mixing and HPT. HPT-deformation experiments of single phase materials are conducted using Polymers (PTFE, PEEK, POM, PVC, PP) and commercial Y35-ferrite ceramics. To study the co-deformation of polymers, copper (Cu) –polymer composites are fabricated by a multi-sector disk approach. In a 2nd step, composites are fabricated using Sr-M-type hexaferrite phase as the hard magnetic component and iron (Fe), copper (Cu), chromium (Cr) and PTFE as a matrix. Furthermore, the effect of HPT deformation on commercial Y35-ferrites and the AlNiCo grades: AlNiCo 3, AlNiCo 5, and AlNiCo 8 are studied. Samples are examined by X-ray difraction (XRD), scanning electron microscopy (SEM), and light microscopy.
The magnetic properties of pristine magnets, deformed Y35-ferrites, powder composites, and deformed AlNiCo alloys are investigated. For magnetic measurements, a hystograph is used. To determine microstructural evolution, commercial Y35-ferrite is annealed at 300 ◦C, 500 ◦C, 700 ◦C, 900 ◦C and 1100 ◦C, under atmospheric conditions and analyzed by XRD and light microscopy. HPT experiments reveal the deformability of bulk polymers to be limited. Properties of PTFE and POM are considered suitable for composite fabrication. Plastic incompatibility of bulk ferrite ceramic with metals and polymers leads to the fabrication of no structurally stable composites, using the multi-sector disc approach. Polymer-metal composites are successfully fabricated using the multi-sector disk approach. Application of post deformation annealing (PDA) combined with pressing increases the adherence between layers in polymer-metal and polymer-ceramic composites. Moreover, powder composites are successfully fabricated with ceramic-metal and ceramic-polymer combinations. Despite a homogeneous distribution and sufficient refining no coupling between the magnetic phases is observed.
The evolution of magnetic and structural properties shows a dependence on the powder combination used and is in good agreement with the literature. HPT of commercial Y35-ferrites leads to a grinding of sintered grains followed by a re-consolidation by pressing and interlocking of particles. These results are in good agreement with the literature.
Annealing experiments show a sufficient stabilized microtructure. In addition, observed substitution effects of calcium (Ca) and aluminum (Al) lead to a shrinkage of the unit cell accompanied by an increase of Hc.