Simulation of alnico coercivity

Ke, Liqin; Skomski, Ralph; Hoffmann, Todd D.; Zhou, Lin; Tang, Wei; Johnson, Duane D.; Kramer, M. J.; Anderson, Iver E.; Wang, C.-Z.

doi:10.1063/1.4992787

Cited by 33 publications

(10 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The difference between theoretically achievable coercivity and experimentally measured values is explained by the diameter of the α 1 phase being much larger than the optimal diameter of the magnetic nano-rods assuming a coherent rotation (2R coh = 12.8 nm) mechanism used in the micromagnetic modeling. [9,26] In situ magnetization in TEM showed that the α 1 rods connected by branches tend reverse at the same external magnetic field, this confirms the modeling that branching segments act as short circuits to domain rotation and allow for a cascading domain reversal at lower applied fields. [26] The EDS mapping clearly shows that the Cu-enriched rods extending along the rod boundaries and in some cases providing additional separation (Fig.…”

Section: Discussionsupporting

confidence: 66%

“…[9,26] In situ magnetization in TEM showed that the α 1 rods connected by branches tend reverse at the same external magnetic field, this confirms the modeling that branching segments act as short circuits to domain rotation and allow for a cascading domain reversal at lower applied fields. [26] The EDS mapping clearly shows that the Cu-enriched rods extending along the rod boundaries and in some cases providing additional separation (Fig. 3).…”

Section: Discussionsupporting

confidence: 66%

See 1 more Smart Citation

Microstructure and coercivity in alnico 9

Zhou

White

et al. 2019

Journal of Magnetism and Magnetic Materials

Self Cite

View full text Add to dashboard Cite

Magnetic property enhancement of alnico, a rare-earth free permanent magnet, is highly dependent on both the initial microstructure and the evolution of the spinodal decomposition (SD) inside each grain during the heat treatment process. The size, shape and distribution of the magnetic FeCo-rich (α1) phase embedded in continuous non-magnetic AlNi-rich (α2) phase as well as a minor Cu-enriched phase residing in between are shown to be crucial in controlling coercivity. Phase and magnetic domain morphology in a commercial alnico 9 alloy was studied using a combination of structural characterization techniques, including scanning electron microscopy, electron backscatter diffraction, aberration-corrected scanning transmission electron microscopy and Lorentz microscopy. Our results showed that casting created structural nonuniformity and defects, such as porosity, TiS2 precipitates and grain misorientation, are heterogeneously distributed, with the center section having the best crystallographic orientation and minimal defects. The optimal spinodal is a "mosaic structure", composed of rod-shape α1 phase with {1 1 0} or {1 0 0} planar faceting and diameter of ∼30-45 nm. There is also a Cu-enriched phase residing at the corners of two 〈1 1 0〉 facets of the α1 phase. It was observed that grain boundary phase reverse magnetization direction at lower external magnetic field compared to the SD region inside the grain. Improving grain orientation uniformity, reducing detrimental grain boundary phase volume fraction, and the branching of the α1 rods, as well as their diameter, are promising routes to improve energy product of alnico.

show abstract

Section: Discussionsupporting

confidence: 66%

Section: Discussionsupporting

confidence: 66%

Microstructure and coercivity in alnico 9

Zhou

White

et al. 2019

Journal of Magnetism and Magnetic Materials

Self Cite

View full text Add to dashboard Cite

show abstract

“…The Cu lattice shearing from the bcc structure may be because the fcc structure of Cu is thermodynamically more stable. Moreover, since some branching types may be very detrimental to H ci , a larger Cu cluster can isolate two originally connected α 1 rods and increases H ci [20]. Finally, formation of small α 1 rods or even chains of spheres, along with the previously reported formation of Ni-rich (α 3 ) separation phase at the α 1 / α 2 interface can also help to increase H ci [21].…”

Section: Discussionmentioning

confidence: 91%

On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

et al. 2018

Self Cite

View full text Add to dashboard Cite

Alnico is a prime example of a finely tuned nanostructure whose magnetic properties are intimately connected to magnetic annealing (MA) during spinodal transformation and subsequent lower temperature annealing (draw) cycles. Using a combination of transmission electron microscopy and atom probe tomography, we show how these critical processing steps affect the local composition and nanostructure evolution with impact on magnetic properties. The nearly 2fold increase of intrinsic coercivity (H ci ) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase (α 1 ) isolation, development of Cu-rich spheres/rods/blades and additional α 1 rod precipitation that occurs during the MA and draw, likely play a key role in H ci enhancement. Chemical ordering of the Al-Ni-phase (α 2 ) and formation of Ni-rich (α 3 ) may also contribute. Unraveling of the subtle effect of these nano-scaled features is crucial to understanding on how to improve shape anisotropy in alnico magnets.

show abstract

“…Any alteration of the spinodal decomposition phenomena during the MA and the concentration of the diffusing species during the lower temperature draw cycles will ultimately impact the magnetic properties. The loss of both Al and Cu was likely a contributor to the observed drop in coercivity as both elements act to separate the Fe-Co rods in the nanostructure; without a high enough concentration of Al and Cu, the Fe-Co rods will no longer be substantially isolated and the coercivity will decrease due to magnetic spin coupling between them [11,12,34,35].…”

Section: Discussionmentioning

confidence: 99%

Processing of Alnico Magnets by Additive Manufacturing

et al. 2019

View full text Add to dashboard Cite

Permanent magnets without rare earth (RE) elements, such as alnico, will improve supply stability and potentially decrease permanent magnet cost, especially for traction drive motors and other increased temperature applications. Commercial alnico magnets with the highest energy product are produced by directional solidification (DS) to achieve a <001> columnar grain orientation followed by significant final machining, adding to the high cost. Additive manufacturing (AM) is an effective method to process near net-shape parts with minimal final machining of complex geometries. AM also, has potential for texture/grain orientation control and compositionally graded structures. This report describes fabrication of alnico magnets by AM using both laser engineered net shaping (LENS)/directed energy deposition (DED) and electron beam melting powder bed fusion (EBM/PBF). High pressure gas atomized (HPGA) pre-alloyed alnico powders, with high purity and sphericity, were built into cylindrical and rectangular samples, followed by magnetic annealing (MA) and a full heat treatment (FHT). The magnetic properties of these AM processed specimens were different from their cast and sintered counterparts of the same composition and show a great sensitivity to heat treatment. The AM process parameters used in this developmental study did not yet result in any preferred texture within the alnico AM builds. These findings demonstrate feasibility for near net-shape processing of alnico permanent magnets for use in next generation traction drive motors and other applications requiring increased operating temperatures and/or complex engineered part geometries, especially with further AM process development for texture control.

show abstract

Simulation of alnico coercivity

Cited by 33 publications

References 40 publications

Microstructure and coercivity in alnico 9

Microstructure and coercivity in alnico 9

On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

Processing of Alnico Magnets by Additive Manufacturing

Contact Info

Product

Resources

About