•Continuous GBPs turn into discrete upon the angle between {0001} planes and GB increases from 0 to 90°, which is owing to the strong texture.•The larger angle between {0001} planes and GBs, the more ...{0001} diffusion channels for atoms to GBs, resulting in discrete and thick GBPs.•Both the GBPs thickness and PFZs width increase linearly by a factor of 2.5–4.•GBPs are alternatively stacked Cu-rich SmCo5 and Zr-rich Smn+1Co5n−1 (n = 2,3,4) compounds, and the PFZs are composed of 2:17R and intermediate 2:17R’ phases.•PFZs are weak pinning sites for magnetic domain walls as revealed by in-situ Lorentz TEM.
In a typical sintered multi-component Sm2Co17-type magnet with strong fiber texture, we show that the distributions of grain boundary precipitates (GBPs) are heavily dependent on the grain boundary (GB) geometry with respect to the texture direction, which has significant effects on domain wall pinning. Results demonstrate that the continuous GBPs turn into discrete upon the angle between {0001} planes and GB increases from 0° to 90°, meanwhile the GBPs thickness and precipitation free zones (PFZs) width both increase linearly by a factor of 2.5–4. Transmission electron microscopy (TEM) reveals that the GBPs are alternatively stacked Cu-rich SmCo5 and Zr-rich Smn+1Co5n−1 (n = 2,3,4) compounds, while the PFZs are composed of 2:17R and intermediate 2:17R’ phases. Atomic-level elemental mappings and first-principles calculations indicate that Cu exists at the Co-2c site in the SmCo5 forming SmCo3Cu2 and Zr locates at the dumbbell Sm-6c sites in the Smn+1Co5n−1. The symbiotic GBPs have orientation relationships of 0001GBPs//00012:17R and 101¯0GBPs//21¯1¯02:17R. The formation of anisotropic GBPs is owing to the strong fiber texture, i.e., the larger angle between {0001} planes and GBs, the more {0001} diffusion channels for atoms to GBs, resulting in discrete and thick GBPs. In-situ Lorentz TEM shows that the domain walls interrupted by GBPs migrate easily under applied magnetic fields. Possible approaches to enhance the magnetic hardness via tuning the GBs are proposed.
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The unavoidably formed rare-earth sesquioxide Sm2O3 microparticles in Sm2Co17-type magnets have been reported to deteriorate magnets’ magnetic properties but improve their mechanical and electrical ...performance. Here, we unveil the distribution, structure and elastic properties of Sm2O3 in a high-end Sm2Co17-type magnet. Results show that Sm2O3 microparticles with size of 4.8 ± 2.1 μm randomly disperse in the magnet, and they serve as the preferential sites for segregation of micron-sized Zr-rich inclusions. Based on Kikuchi lines and atomic images, the Sm2O3 is indexed to be the metastable trigonal A-type (P3¯m1) rather than the monoclinic B-type (C2/m) or stable cubic C-type (Ia3¯). The trigonal Sm2O3 is nano-twinned with twin boundaries of {2¯110} planes. Calculated elastic constants suggest that the trigonal Sm2O3 is ductile and could be an effective phase to reduce the brittleness of the magnet. Our work may offer insights for alleviating the trade-off between magnetic and mechanical properties of Sm2Co17-type magnets.
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•Profuse lamellar-type microstructures were found in the solution-treated Sm(CobalFe0.31Cu0.07Zr0.025)7.7 magnets. Within the lamellar-type microstructure, there are three microregions exhibiting an ...obvious difference in composition and 2:17R ordering degree.•TEM images indicate the 1:3R phase may have precipitated and then re-dissolved during the solution treatment.•A long-time solution treatment under appropriate temperature could enhance the compositional uniformity and promote the transformation from 2:17R phase to 1:7H phase.
The solution-treated Fe-rich 2:17-type Sm-Co-based magnets generally contain an inhomogeneous microstructure, which hinders the development of the complete cellular structure required for high-performance magnets. Here, the microstructure evolution of Sm(CobalFe0.31Cu0.07Zr0.025)7.7 magnet during the solution treatment is systematically investigated. Unlike the normal Fe-medium magnets, it was interestingly found that the initial-stage solution-treated Sm(CobalFe0.31Cu0.07Zr0.025)7.7 magnet possesses a profuse lamellar-type microstructure. Within the lamellar-type microstructure, there are three microregions exhibiting an obvious difference in composition and 2:17R ordering degree. Further, various 1:3R phases precipitated within the lamellar-type microstructure. With the disappearance of lamellar-type microstructure, the 1:7H phase increased substantially, and the distribution of defect-aggregated cell boundaries became uniform, promoting the homogeneous precipitation of 1:5H cell boundary phases during aging. The current study reveals a typical microstructural evolution in Fe-rich 2:17-type Sm-Co-based magnets during solution treatment.
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