Periodic Reporting for period 4 - SpdTuM (SPD nanostructured magnets with tuneable properties)
Periodo di rendicontazione: 2022-07-01 al 2023-12-31
Nanostructured magnets have been the focus of research since two decades. One of the remaining key challenges is to synthesize bulk nanostructured magnets of a reasonable size. Heavy plastic deformation, usually called severe plastic deformation (SPD), is one innovative, large scale processing route to synthesize bulk nanostructured materials in large dimensions and novel SPD setups for samples sizes up to a diameter of 60 mm and thickness of 12 mm have become available recently.
In this project, the potential to fabricate bulk nanostructured magnets by SPD as novel processing route was investigated. The aim of the project was to synthesize different nanostructured magnets by SPD as well as to tailor their microstructure to attain the desired magnetic properties. The SPD process has the advantage that bulk nanostructured magnets with a well-defined composition can be manufactured and the starting materials used can be manifold. By using powder blends, almost unlimited materials combinations beyond the equilibrium phase diagram were realized. Using the latter, the magnetic properties of SPD processed nanostructures materials were modified in wide range by subsequent thermal treatments. By using different material combinations and thermal treatments, unique nanostructures were obtained and the magnetic properties were optimized.
The increase of global energy consumption and growing demand for renewable energy necessitates hard magnetic materials (permanent magnets) with high energy products. Up-to-date hard magnets are mainly composed of rare earth transition metals and excellent magnetic properties close to theoretical predictions are already reached. However, the prize of rare earth elements is interconnected to politic instabilities in the countries of their origin, which often establish a monopoly market. Thus, an innovative field of research covers the partial or full replacement of rare earth metals in hard magnetic materials with the aim that they are still maintaining their high energy product and their excellent performance.
One promising research approach is to induce exchange coupling between hard and a soft magnetic phases in nanocomposite magnets. The required magnetic anisotropy is provided by the hard phase. It further stabilizes the exchange coupled soft magnetic phase against demagnetization, which leads to a high coercivity. The soft magnetic phase makes its high magnetization available, which is necessary for remanence enhancement. By selecting different magnetic starting materials, such as soft, hard and antiferromagnetic-ferromagnetic powders, different types of these nanocomposite magnets were synthesized by SPD in this project.
The project finally included fine tuning of the microstructure and resulting magnetic properties through adjustments in the composition of the magnetic phases, SPD processing parameters and annealing treatments. To achieve these goals, in-depth microstructural characterization was performed. Simultaneously, the magnetic properties were measured, which help to gain a deeper understanding to improve the performance of SPD processed nanostructured magnets.
In this project, the potential to fabricate bulk nanostructured magnets by SPD as novel processing route was investigated. The aim of the project was to synthesize different nanostructured magnets by SPD as well as to tailor their microstructure to attain the desired magnetic properties. The SPD process has the advantage that bulk nanostructured magnets with a well-defined composition can be manufactured and the starting materials used can be manifold. By using powder blends, almost unlimited materials combinations beyond the equilibrium phase diagram were realized. Using the latter, the magnetic properties of SPD processed nanostructures materials were modified in wide range by subsequent thermal treatments. By using different material combinations and thermal treatments, unique nanostructures were obtained and the magnetic properties were optimized.
The increase of global energy consumption and growing demand for renewable energy necessitates hard magnetic materials (permanent magnets) with high energy products. Up-to-date hard magnets are mainly composed of rare earth transition metals and excellent magnetic properties close to theoretical predictions are already reached. However, the prize of rare earth elements is interconnected to politic instabilities in the countries of their origin, which often establish a monopoly market. Thus, an innovative field of research covers the partial or full replacement of rare earth metals in hard magnetic materials with the aim that they are still maintaining their high energy product and their excellent performance.
One promising research approach is to induce exchange coupling between hard and a soft magnetic phases in nanocomposite magnets. The required magnetic anisotropy is provided by the hard phase. It further stabilizes the exchange coupled soft magnetic phase against demagnetization, which leads to a high coercivity. The soft magnetic phase makes its high magnetization available, which is necessary for remanence enhancement. By selecting different magnetic starting materials, such as soft, hard and antiferromagnetic-ferromagnetic powders, different types of these nanocomposite magnets were synthesized by SPD in this project.
The project finally included fine tuning of the microstructure and resulting magnetic properties through adjustments in the composition of the magnetic phases, SPD processing parameters and annealing treatments. To achieve these goals, in-depth microstructural characterization was performed. Simultaneously, the magnetic properties were measured, which help to gain a deeper understanding to improve the performance of SPD processed nanostructured magnets.
The results of the project showed that the SPD technique is a promising processing route to obtain novel nanostructured materials with extraordinary magnetic properties. Different nanostructured materials have been investigated so far. The first group of magnetic materials includes materials of different mutually immiscible components, which become either nanostructured supersaturated alloys or nanocomposites with partial supersaturation after SPD, both not producible by classical metallurgical ways. By combining magnetic and non-magnetic elements, SPD and phase separation during subsequent thermal treatments, unique nanostructures consisting of finely dispersed magnetic and non-magnetic phases were achieved. After SPD, microstructural and magnetic investigations were performed and a significant improvement in the understanding of the structure and resulting magnetic properties in these nanostructured magnets have been obtained.
However, the most important magnetic properties from a future application viewpoint are magnetoresistive and magnetostrictive properties. Thus, detailed investigations on the influence of processing parameters and material compositions on the magneto-resistance were performed in the Cu-Co and Cu-Fe system. In both alloy systems, the granular magneto-resistivity can be correlated to the ferromagnetic particle size, making the effect extremely sensitive to the processing method and annealing treatments.
The focus of the second part of the project was on manufacturing different types of hard magnetic materials and nanocomposites by SPD, in which we have significantly improved the SPD processing knowledge and the underlying phenomena of microstructural evolution during SPD of these type of materials. Two main approaches were used. First, magnetic coupling effects, namely ’exchange bias’ and ’exchange coupling’, were investigated. Second, the synthesis of a rare-earth free ferro-magnetic phase, α-MnBi, was in focus.
However, the most important magnetic properties from a future application viewpoint are magnetoresistive and magnetostrictive properties. Thus, detailed investigations on the influence of processing parameters and material compositions on the magneto-resistance were performed in the Cu-Co and Cu-Fe system. In both alloy systems, the granular magneto-resistivity can be correlated to the ferromagnetic particle size, making the effect extremely sensitive to the processing method and annealing treatments.
The focus of the second part of the project was on manufacturing different types of hard magnetic materials and nanocomposites by SPD, in which we have significantly improved the SPD processing knowledge and the underlying phenomena of microstructural evolution during SPD of these type of materials. Two main approaches were used. First, magnetic coupling effects, namely ’exchange bias’ and ’exchange coupling’, were investigated. Second, the synthesis of a rare-earth free ferro-magnetic phase, α-MnBi, was in focus.
SPD processing might facilitate the use of advanced magnetic materials as widespread industrial components in the future. The advantages of SPD processing of magnetic materials are:
- additional increase in coercivity by decreasing microstructural feature sizes;
- deformation-induced texture leads to anisotropic magnetic properties;
- metastable phase formation during processing;
- possibility to combine completely different processing steps (powder compaction (equivalent to sintering), grain refinement and texturing) in one step;
- HPT deformed materials with large defect densities can be uses as pre-material for subsequent annealing treatments with enhanced phase formation kinetics.
By successful processing of magnetic nanocomposites by SPD, stronger and smaller magnets might be obtained. In turn, that would enable the design of smaller devices that are more energy efficient. Less or even no rare-earth elements are needed in SPD processed SmCo and α-MnBi magnetic nanocomposites as well as in ferromagnetic-antiferromagnetic composites. Thus, these magnetic materials would be cheaper. Furthermore, the saving of rare-earth elements would help to avoid sourcing problems.
Finally, first results have shown that there is also plenty of room for fabrication of innovate magnetic materials by a combination of SPD processing with other synthesis methods (ball milling, arc melting). It would open up the well-known powder processing routes to produce highly tuned magnetic materials by design.
- additional increase in coercivity by decreasing microstructural feature sizes;
- deformation-induced texture leads to anisotropic magnetic properties;
- metastable phase formation during processing;
- possibility to combine completely different processing steps (powder compaction (equivalent to sintering), grain refinement and texturing) in one step;
- HPT deformed materials with large defect densities can be uses as pre-material for subsequent annealing treatments with enhanced phase formation kinetics.
By successful processing of magnetic nanocomposites by SPD, stronger and smaller magnets might be obtained. In turn, that would enable the design of smaller devices that are more energy efficient. Less or even no rare-earth elements are needed in SPD processed SmCo and α-MnBi magnetic nanocomposites as well as in ferromagnetic-antiferromagnetic composites. Thus, these magnetic materials would be cheaper. Furthermore, the saving of rare-earth elements would help to avoid sourcing problems.
Finally, first results have shown that there is also plenty of room for fabrication of innovate magnetic materials by a combination of SPD processing with other synthesis methods (ball milling, arc melting). It would open up the well-known powder processing routes to produce highly tuned magnetic materials by design.