Effects of Titanium in Alnico 8-Type Magnet Alloys

“…Using advanced characterization and simulation tools [11][12][13][14][15][16][17][18][19], in particular aberrationcorrected scanning transmission electron microscopy (STEM) and in-situ Lorentz microscopy, we describe the crucial microstructure and magnetization features of a commercial alnico 9 that give rise to the highest energy product of ~10.5MGOe in the alnico family. Armed with this information, key processing and chemical modifications are proposed for further improving the energy product of alnico [20] .…”

Section: Introductionmentioning

confidence: 99%

Microstructure and coercivity in alnico 9

Zhou

White

et al. 2019

Journal of Magnetism and Magnetic Materials

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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.

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“…As a result, magnetic properties of alnico strongly depend on the details of its unique microstructure: a periodically arrayed elongated Fe-Co rich (α 1 ) hard magnetic phase embedded in a continuous non-magnetic Ni-Al-rich (α 2 ) matrix, formed via SD. Achieving the optimum properties in alnico requires a well controlled and lengthy heat-treatment process, including solutionization of the alloy above 1200 • C, isothermal MA near its Curie temperature and subsequent lower temperature annealing (draw cycles) [1,[8][9][10][11][12]. The application of MA marks the most important cornerstone in alnico magnets' development history.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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.

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Effects of Titanium in Alnico 8-Type Magnet Alloys

Cited by 24 publications

References 5 publications

Spinodal Decomposition in Alnico 8 Magnet Alloy

Spinodal Decomposition in Alnico 8 Magnet Alloy

Microstructure and coercivity in alnico 9

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

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