Magnets are key materials for the electrification of mobility and also for the generation and transformation of electric energy. Research and development in recent decades lead to high performance magnets, which require a finely tuned microstructure to serve applications with ever increasing requirements. Besides optimizing already known materials and the search on novel material combinations, an increasing interest in unconventional processing techniques and the utilization of magnetic concepts is apparent. Severe plastic deformation (SPD), in particular by high-pressure torsion (HPT) is a versatile and suitable method to manufacture microstructures not attained so far, but entitling different magnetic coupling mechanisms fostering magnetic properties. In this work, we review recent achievements obtained by HPT on soft and hard magnetic materials, focusing on powder as starting materials. Furthermore, we give specific attention to the formation of magnetic composites and highlight the opportunities of powder starting materials for HPT to exploit magnetic interaction mechanisms.

In our search for an optimum soft magnet with excellent mechanical properties which can be used in applications centered around “electro mobility”, nanocrystalline CoCrFeNiGa_x (x = 0.5, 1.0) bulk high entropy alloys (HEA) were successfully produced by spark plasma sintering (SPS) at 1073 K of HEA powders produced by high energy ball milling (HEBM). SPS of non-equiatomic CoCrFeNiGa_0.5 particles results in the formation of a single-phase fcc bulk HEA, while for the equiatomic CoCrFeNiGa composition a mixture of bcc and fcc phases was found. For both compositions SEM/EDX analysis showed a predominant uniform distribution of the elements with only a small number of Cr-rich precipitates. High pressure torsion (HPT) of the bulk samples led to an increased homogeneity and a grain refinement: i.e., the crystallite size of the single fcc phase of CoCrFeNiGa_0.5 decreased by a factor of 3; the crystallite size of the bcc and fcc phases of CoCrFeNiGa—by a factor of 4 and 10, respectively. The lattice strains substantially increased by nearly the same extent. After HPT the saturation magnetization (M_s) of the fcc phase of CoCrFeNiGa_0.5 and its Curie temperature increased by 17% (up to 35 Am²/kg) and 31.5% (from 95 K to 125 K), respectively, whereas the coercivity decreased by a factor of 6. The overall M_s of the equiatomic CoCrFeNiGa decreased by 34% and 55% at 10 K and 300 K, respectively. At the same time the coercivity of CoCrFeNiGa increased by 50%. The HPT treatment of SPS-consolidated HEAs increased the Vickers hardness (H_v) by a factor of two (up to 5.632 ± 0.188) only for the non-equiatomic CoCrFeNiGa_0.5, while for the equiatomic composition, the H_v remained unchanged (6.343–6.425 GPa).

The possibilities of nanoadditivation to achieve finer, more equiaxed grains unlock huge potential for the application field of functional materials, e.g. Nd-Fe-B magnets, where the control of the microstructure and the composition is of significant importance. The surface modification of hard magnetic microparticles by non-magnetic nanoparticles (NPs) opens a novel field of research. Here, especially Cu NPs with low amounts of oxides are of high relevance as colloidal nano-additive material. To increase the productivity of surfactant-free, laser-generated Cu NPs, we performed a process parameter study via laser ablation in acetone aiming for the highest possible productivity, increasing the throughput of NP additivation on the surface of functional feedstock micro powders. By optimizing the process parameters of laser power, laser fluence, repetition rate, volume flow, and spot size, a productivity of 0.19 µg/J of Cu NPs in acetone was achieved. Then we investigated how a fine microstructure of the magnet powder MQP-S can be retained to some extent along the process chain, throughout the melting and resolidification process during suction casting. A loading series of Cu NP nanoadditivation on magnet micro powders of 0.1, 0.5, 1.0, and 2.5 wt.% was analyzed regarding magnetic properties and microstructure of the as-built part. Using full melting conditions of MQP-S by producing samples via suction casting modified with different amounts of Cu NP additions leads to finer grains, but increasing α-Fe content. Overall, the results enable higher production rates of Cu NPs in acetone and provide insights into the influence of NP-supporting characteristics on the properties of permanent magnet micro powders after full melting and resolidification.