On the ε → τ phase transformation and twinning in L10−MnAl alloys

Jia, Yan; Ding, Huang; Wu, Yuehong; Wang, Jingmin; Wu, Haichen; Ma, Tianyu; Zhao, Shiteng; Skokov, Konstantin P.; Aubert, Alex; Maccari, Fernando; Gutfleisch, Oliver; Xu, Yichen; Niu, Jiejue; Qiao, Boying; Zhao, Shuang; Jiang, Chengbao

doi:10.1016/j.actamat.2022.117892

Cited by 17 publications

(20 citation statements)

References 72 publications

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“…3a, in which two peaks respectively at ~76° and ~84° are detected. According to previous investigations by Bittner, Zhao, Jia et al 45,47,50 , they correspond to true twins and order twins, respectively. Using the two featured misorientation angles as criterion, the twin boundaries can be distinguished basing on EBSD analysis, as illustrated by red lines and curves in Fig.…”

Section: Resultsmentioning

confidence: 85%

“…Two twin-variants are detected, the twinning plane is proved to be (111) τ . The orientation difference between the two variants is ~76 o , corresponding to the true twins 45,50,51 . High-resolution TEM (HRTEM) image (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…near the temperature at which the ε → τ phase transformation is triggered, a significantly enhanced [001]τ texture can be realized, the remanence ratio is also increased to ~0.64 45,48 . Compared to the strategies described above, texture improvement through the usage of twin-free particles results in remanence ratio of ~0.70, which is an unprecedented value for MnAl polymer bonded magnets.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, for polycrystalline samples with twin-free grains, strong [001]τ texture is still required to obtain high remanence. Our previous work demonstrates that, ε → τ transformation triggered by thermal-mechanical-coupled field can result in grain refinement and [001]τ preferred texture 45,51 . If the grain size can be decreased to the optimal range, twins are expected to be eliminated.…”

Section: Stb-surface Area Of Twin Boundarymentioning

confidence: 99%

“…However, twins are scarcely eliminated by conventional fabrication methods (e.g. melt spinning 45 , ball milling 44 , sintering 33 , hot deformation 47,48 , gas atomization 30 , etc. ), leading to a great gap between the actual properties and the theoretical properties especially in remanence and energy products (see Fig.…”

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confidence: 99%

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Roadmap towards optimal magnetic properties in rare-earth-free L10-MnAl permanent magnets

Jia

et al. 2022

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Twin defects deteriorate the magnetic properties in conventionally-fabricated L10-type and RETM12-type permanent magnets. Herein, we propose a strategy to suppress twins’ formation by decreasing the grain and/or particle sizes below a critical size Dt~300 nm, based on the stress relief mechanism resulting from the balance of volume/surface energy. Twin-free monocrystalline nanoparticles smaller than Dt were synthesized using a comprehensive spectrum of methods for preparing field-aligned polymer bonded magnet with high texture. We propose here a roadmap for selecting the best route for manufacturing high-performance rare-earth free MnAl magnets, depending on their grain/particle size. The dependence of coercivity on grain/particle sizes shows that optimal coercivity can be reached within the range of 50-200 nm, meanwhile, twin-free microstructure is realized which allows ultrahigh remanence by field induced texture. The results reported here can be applied to other twin-containing permanent magnet compounds, offering opportunities to drastically increase their texture and maximal energy products.

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Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Stb-surface Area Of Twin Boundarymentioning

confidence: 99%

mentioning

confidence: 99%

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Roadmap towards optimal magnetic properties in rare-earth-free L10-MnAl permanent magnets

Jia

et al. 2022

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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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Atomic Migration and Ordering of Binary Ferromagnetic Intermetallic L1₀Phases and Influences of Alloying Elements and Electric Fields

2023

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The ordered body‐centered tetragonal intermetallic phase of FeNi is a promising candidate for high‐performance permanent magnets without rare‐earth elements. However, on earth FeNi is found naturally only in the disordered face‐centered‐cubic A1 phase. Herein, the atomic migration and ordering processes in binary intermetallic phases are investigated within the framework of density‐functional theory. The main objectives are 1) to develop a thorough understanding of the thermally activated diffusion processes at the atomic scale and 2) to make a critical assessment in how far electric field and current effects can be effective means for an enhanced hardening‐by‐ordering of disordered, soft‐ferromagnetic alloys. The scope is extended from FeNi to the hard‐ferromagnetic phases of FePt, FePd, MnAl, and MnGa as well as ternary Fe(Pt,Ni) alloys. These materials cover a wide range of thermal‐ordering time scales and related experimental feasibility.

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On the ε → τ phase transformation and twinning in L10−MnAl alloys

Cited by 17 publications

References 72 publications

Roadmap towards optimal magnetic properties in rare-earth-free L10-MnAl permanent magnets

Roadmap towards optimal magnetic properties in rare-earth-free L10-MnAl permanent magnets

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

Atomic Migration and Ordering of Binary Ferromagnetic Intermetallic L1₀Phases and Influences of Alloying Elements and Electric Fields

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On the ε → τ phase transformation and twinning in L10−MnAl alloys

Cited by 17 publications

References 72 publications

Roadmap towards optimal magnetic properties in rare-earth-free L10-MnAl permanent magnets

Roadmap towards optimal magnetic properties in rare-earth-free L10-MnAl permanent magnets

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

Atomic Migration and Ordering of Binary Ferromagnetic Intermetallic L10Phases and Influences of Alloying Elements and Electric Fields

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Product

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

Atomic Migration and Ordering of Binary Ferromagnetic Intermetallic L1₀Phases and Influences of Alloying Elements and Electric Fields