Microstructure and magnetic properties of Mn-Al-C permanent magnets produced by various techniques

Popov, V. V.; Maccari, Fernando; Radulov, I.; Kovalevsky, A. A.; Katz‐Demyanetz, Alexander; Bamberger, Μ.

doi:10.1051/mfreview/2021008

Cited by 9 publications

(6 citation statements)

References 44 publications

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“…In the literature, two methods are commonly reported: (i) slow cooling from the high temperature -phase or (ii) rapid cooling (i.e. quenching) from the melt or from the -phase followed by an annealing process at moderate temperatures (450-600 C) [11][12][13]. It is worth mentioning that the cooling rate in (i) or a long time annealing in (ii) can lead to the decomposition of the s-phase into the stable phases.…”

Section: Graphical Abstract Introductionmentioning

confidence: 99%

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

et al. 2022

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Mn–Al–C is intended to be one of the “gap magnets” with magnetic performance in-between ferrites and Nd-Fe-B. These magnets are based on the metastable ferromagnetic $$\tau$$ τ -phase with L1$$_0$$ 0 structure, which requires well controlled synthesis to prevent the formation of secondary phases, detrimental for magnetic properties. Here, we investigate the formation of $$\tau$$ τ -phase in Mn–Al–C using Spark Plasma Sintering (SPS) and compare with conventional annealing. The effect of SPS parameters (pressure and electric current) on the phase formation is also studied. Single $$\tau$$ τ -phase is obtained for annealing 5 min at $$500~^\circ \hbox {C}$$ 500 ∘ C with SPS. In addition, we show that the initial grain size of the $$\epsilon$$ ϵ -phase is influencing the $$\tau$$ τ -phase transformation and fraction at a given annealing condition, independently of the annealing method used. A faster transformation was observed for smaller initial $$\epsilon$$ ϵ -grains. The samples obtained by SPS showed comparable magnetic properties with the conventional annealed ones, reaching coercivity of 0.18 T and saturation magnetization of 114 Am$$^2$$ 2 /kg in the optimized samples. The similarity in coercivity is related to the microstructure, as we reveal the presence of structure defects like twin boundaries and dislocations in both materials. Graphical abstract

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Section: Graphical Abstract Introductionmentioning

confidence: 99%

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

et al. 2022

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“…However, enhanced diffusion processes due to HPT-induced lattice defects drastically reduces annealing times to a few days, which is stronger pronounced for fine powders. Using HPT processing for Mn-Al-C based permanent magnets is further proposed by Popov et al [132] When deforming the τphase a strong increase of Hc with increasing radius and thus applied strain is found (from 0.22 T up to 0.58 T). In addition, a stress-driven phase transformation of the metastable τ-phase into the β-phase was reported.…”

Section: Hpt-deformation Of Powders To Obtain Hard Magnetic Materialsmentioning

confidence: 99%

Magnetic Materials via High-Pressure Torsion of Powders

et al. 2023

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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 mechanism.

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“…[32,33] It is known that coercivity, being an extrinsic property, it is sensitive to microstructure and, specifically in Mn-Al compounds, it is often linked to the many possible defects resulting from the processing route and from the phase-transformation mechanism, as will be discussed in more detail in Section 2.3 focused on microstructural analysis. [17,25,[33][34][35][36][37]…”

Section: Effect Of Current Density On the ε ! τ Phase Transitionmentioning

confidence: 99%

Ferromagnetic Mn–Al–C L1₀ Formation by Electric Current Assisted Annealing

et al. 2023

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The ferromagnetic Mn–Al–C τ‐phase ( tetragonal structure) shows intrinsic potential to be developed as a permanent magnet; however, this phase is metastable and is easily decomposed to nonmagnetic stable phases, affecting negatively the magnetic properties. Giving the necessity to careful control of its synthesis, the use of a novel approach is investigated using electric current–assisted annealing to obtain pure τ‐phase samples. The temperature and electrical resistance of the samples are monitored during annealing and it is shown that the change in resistance can be used to probe the phase transformation. Upon increase of electric current density, the required temperature for the ferromagnetic phase formation is reduced, reaching a maximum shift of 140 °C at 45 A mm−2. Even though this noticeable shift is achieved, the magnetic properties are not affected showing coercivity of 0.13 T and magnetization of 90 Am2 kg−1, independently from the electric current density used during annealing. Microstructural investigation reveals the nucleation of the τ‐phase at the grain boundaries of the parent ε‐phase. In addition, the existence of twin boundaries upon nucleation and growth of the metastable phase for all evaluated annealing conditions is observed, resulting in similar extrinsic magnetic properties.

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Microstructure and magnetic properties of Mn-Al-C permanent magnets produced by various techniques

Cited by 9 publications

References 44 publications

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

Magnetic Materials via High-Pressure Torsion of Powders

Ferromagnetic Mn–Al–C L1₀ Formation by Electric Current Assisted Annealing

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Microstructure and magnetic properties of Mn-Al-C permanent magnets produced by various techniques

Cited by 9 publications

References 44 publications

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

Magnetic Materials via High-Pressure Torsion of Powders

Ferromagnetic Mn–Al–C L10 Formation by Electric Current Assisted Annealing

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Ferromagnetic Mn–Al–C L1₀ Formation by Electric Current Assisted Annealing