Experimental study on modulated structure in Alnico alloys under high magnetic field and comparison with phase-field simulation

Sun, Xiaofeng; Chen, C.L.; Li, Yang; Lv, Liangxing; Atroshenko, S. A.; Shao, Wen‐Zhu; Sun, Xiaohan; Zhen, Liang

doi:10.1016/j.jmmm.2013.07.050

Cited by 21 publications

(3 citation statements)

References 24 publications

(27 reference statements)

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“…This has profound implications when an applied magnetic field is used to bias growth directions of the a 1 phase. [17] B. Heat-Treated Commercial Alnico 8…”

Section: A Standard Production Commercial Alnicomentioning

confidence: 99%

Role of the Applied Magnetic Field on the Microstructural Evolution in Alnico 8 Alloys

Zhou

Miller

Dillon

et al. 2014

Metallurgical and Materials Transactions E

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“…This has profound implications when an applied magnetic field is used to bias growth directions of the a 1 phase. [17] B. Heat-Treated Commercial Alnico 8…”

Section: A Standard Production Commercial Alnicomentioning

confidence: 99%

Role of the Applied Magnetic Field on the Microstructural Evolution in Alnico 8 Alloys

Zhou

Miller

Dillon

et al. 2014

Metallurgical and Materials Transactions E

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“…The magnetic properties of alnico alloys are highly linked to the nanostructure formed during a rapidly quenched, phase decomposition process, in which a single α phase (body centered cubic structure) from solid solution at ~1,250°C is decomposed into an Fe–Co-rich α 1 hard magnetic phase, and a non-magnetic Ni–Al-rich α 2 phase. External magnetic field annealing at ~800°C can increase the magnetic properties by tuning the nanostructures (Chu et al, 2000; Sun et al, 2013; Zhou et al, 2014 a ). In addition, recent experiments and theoretical predictions on alnico alloys indicate that further improvements require subtle changes in chemistry and processing to reduce the diameter of α 1 phases (Zhou et al, 2014 a ).…”

Section: Introductionmentioning

confidence: 99%

Correlative Energy-Dispersive X-Ray Spectroscopic Tomography and Atom Probe Tomography of the Phase Separation in an Alnico 8 Alloy

et al. 2016

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Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology and volume fractions of Fe-Co-rich and Νi-Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2-4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.

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“…It is possible our samples had not reached the point of refinement in the same time frame as Chu's; however, magnetic anneals ranging from 15-30 minutes have been performed on the same material and do not show any evidence of refinement. Other considerations are the difference in applied field strength of 1 T compared to 0.34 T, though it has been shown that this difference in field strength has relatively little effect on microstructure[3],[54].…”

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confidence: 99%

Effects of heat treatment and processing modifications on microstructure in alnico 8H permanent magnet alloys for high temperature applications

Dillon¹

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2014ii In addition, I would like to thank my friends, family, and loved ones for their endless encouragement and love during my college career. ABSTRACTAlnico is a commercially available series of permanent magnet alloys, which form a nanoscale bcc-intermetallic spinodally decomposed structure. The major mechanism of coercivity in these alloys is shape anisotropy produced by the spinodal morphology. A series of heat treatments, with and without external magnetic field, is crucial to developing optimal magnetic properties. Alnico 8H has a coercivity of 1900 Oe, the highest of all commercial alnico grades, and was used to investigate heat treatment effects on microstructure and magnetic properties.Conventional alnico 8H permanent magnets are manufactured by casting or sintered blended elemental powder techniques. Oxides, especially in sintered varieties, can make up as much as 4% of the magnet, reducing total magnetization. Detrimental grain boundary γ phase, and a newly observed σ phase are present in finished commercial magnets, reducing coercivity. Intragranular γ was also found in sintered varieties. Growth of γ occurred as much as 200°C below its reported thermodynamically stable temperature, as shown in recent phase diagrams.Pre-alloyed alnico 8H (without minor Si, S, or Nb additions) was gas atomized into fine single-phase spherical powders to investigate alternative consolidation methods and processing routes. Hot isostatic pressing at 1250°C produces a fully dense compact with small amounts of γ phase and very a low oxide content. Heat-treating in a similar manner to commercial alnico yields a maximum energy product slightly exceeding standard commercial values. Spark plasma sintering (SPS) at lower temperatures generates compacts 80-92% dense, with a large intercellular network of γ and σ phases.

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Experimental study on modulated structure in Alnico alloys under high magnetic field and comparison with phase-field simulation

Cited by 21 publications

References 24 publications

Role of the Applied Magnetic Field on the Microstructural Evolution in Alnico 8 Alloys

Role of the Applied Magnetic Field on the Microstructural Evolution in Alnico 8 Alloys

Correlative Energy-Dispersive X-Ray Spectroscopic Tomography and Atom Probe Tomography of the Phase Separation in an Alnico 8 Alloy

Effects of heat treatment and processing modifications on microstructure in alnico 8H permanent magnet alloys for high temperature applications

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