Abstract 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.

中文翻译：

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Alnico 9 的微观结构和矫顽力

摘要 Alnico 是一种不含稀土的永磁体，其磁性能的增强高度依赖于初始微观结构和热处理过程中每个晶粒内部的旋节线分解 (SD) 的演变。嵌入在连续非磁性富铝镍 (α2) 相中的磁性富 FeCo (α1) 相的尺寸、形状和分布以及位于两者之间的少量富铜相对于控制矫顽力至关重要。使用结构表征技术的组合，包括扫描电子显微镜、电子背散射衍射、像差校正扫描透射电子显微镜和洛伦兹显微镜，研究了商业 alnico 9 合金中的相和磁畴形态。我们的结果表明，铸造产生的结构不均匀性和缺陷，如孔隙、TiS2 析出和晶粒取向错误，是不均匀分布的，中心部分具有最佳的结晶取向和最少的缺陷。最佳的旋节线是“镶嵌结构”，由具有 {1 1 0} 或 {1 0 0} 平面刻面和直径约 30-45 nm 的棒状 α1 相组成。在 α1 相的两个〈1 1 0〉面的拐角处还有一个富铜相。观察到与晶粒内部的 SD 区域相比，晶界相在较低的外部磁场下反向磁化方向。提高晶粒取向均匀性，减少有害的晶界相体积分数，α1 棒的分支，以及它们的直径，