HoMMage – Hysteresis design by nanostructural-engineering through continuous forming processes
Powerful permanent magnets are considered an important factor in the current discussion on energy efficiency. In order to improve the properties of permanent magnets, the HoMMage project is generating the microstructure by forming metal-matrix composites.
Permanent magnetic materials play an increasingly important role for technologies in the fields of energy generation, mobility, as well as in automation and entertainment industry. The production of permanent magnets has taken a strong upturn in the last decade, and the demand for magnets has increased dramatically due to the increasing automation, as well as the change from combustion engines to electro mobility.
The microstructure of the material is decisive for the outstanding permanent magnetic properties. The main phase (grains) should be surrounded respectively magnetically decoupled by another phase (grain boundary). Both phases should have certain properties to induce magnetization mechanisms, such as domain-wall-pinning or nucleation. In addition, numerous parameters, such as the orientation and size of the grains and the thickness of the grain boundary, have an effect on the magnetic properties.
Current approaches of investigating and manufacturing micro- or nano-structural functional materials are based on melt or powder metallurgy as well as chemical synthesis. These methods are only applicable for specific alloys or material combinations, as they are depending on the phase diagram or chemical properties. Dimensions of the microstructures are also limited by these methods.
Forming of so-called Metal-Matrix-Composites (MMCs) presents a promising solution to overcome these limits. MMCs consist of a matrix and at least one other different material embedded into the matrix. The MMCs studied in the project are composed of wires and a surrounding matrix material. The wires have the composition of the main phase of the magnetic material and are transferred to the desired nanostructure during the forming operations. They are surrounded by a shell material in the form of bundled wires, matrix or coating, which represents the second phase or rather grain boundary phase in the targeted nanostructure. The initial rods will be continuously formed into wires with significantly smaller diameters. These new wires are bundled into rods and formed into wires again. This step will be repeated until the microstructures of the wires have reached the desired dimension, as it shown in Fig. 1.
The approach of engineering the nanoscale MMC cross-sectional structure opens a novel route to investigate in detail the curing mechanisms of nucleation and domain-wall-pinning through the scalability of nanostructure design. At the same time, the mechanisms of plastic deformation and grain refinement of non-conventional forming materials are investigated.
The project is funded by “Deutsche Forschungsgemeinschaft” (DFG) in terms of the Collaborative Research Centre/Transregio (CRC/TRR) 270 – Subproject A09 “Hysteresis design of magnetic materials for efficient energy conversion (HoMMage)”.
Collaborative Research Center