Microstructure and coercivity in alnico 9

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

卷:471

Article

Zhou, Lin¹  White, Emma¹  Ke, Liqin¹  Cullen, David A.²  Lu, Ping³  Constantinides, S.⁴  McCallum, R. W.¹  Anderson, I. E.¹  Kramer, M. J.¹ 

[1] Ames Lab, Ames, IA 50014 USA

[2] Oak Ridge Natl Lab, Mat Sci & Technol Div, Oak Ridge, TN 37831 USA

[3] Sandia Natl Labs, POB 5800,MS 1411, Albuquerque, NM 87185 USA

[4] Arnold Magnet Technol Corp, Rochester, NY 14625 USA

关键词: Permanent magnets;    Microstructure;    Spinodal decomposition;    Atom-probe tomography;    TEM;    STEM HAADF;    Lorentz microscopy;   

DOI  :  10.1016/j.jmmm.2018.09.085

来源: Elsevier

【 摘 要 】

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 (alpha(1)) phase embedded in continuous non-magnetic AlNi-rich (alpha(2)) 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 alpha(1) phase with {1 1 0} or {1 0 0} planar faceting and diameter of similar to 30-45 nm. There is also a Cu-enriched phase residing at the corners of two <1 1 0> facets of the alpha(1) 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 alpha(1) rods, as well as their diameter, are promising routes to improve energy product of alnico.

【 授权许可】

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