Sm2Co17磁体胞状组织边缘2:17R'相的透射电子显微镜表征
收稿日期: 2020-10-16
修回日期: 2021-02-02
网络出版日期: 2021-03-03
基金资助
国家自然科学基金项目(52071256);金属材料强度国家重点实验室开放课题项目(20192106)
Identification of 2:17R' Cell Edge Phase in Sm2Co17-Type Permanent Magnets by Transmission Electron Microscopy
Received date: 2020-10-16
Revised date: 2021-02-02
Online published: 2021-03-03
Supported by
National Natural Science Foundation of China(52071256);Open Project of State Key Laboratory for Mechanical Behavior of Materials(20192106)
结合电子衍射、TEM明/暗场像和HRTEM像从[100]2:17R和[101]2:17R 2个晶带轴研究了具有纳米胞状组织的Sm25Co50.2Fe16.2Cu5.6Zr3.0 (质量分数，%)钉扎型磁体胞边缘的微结构。结果表明，胞状组织边缘存在菱方结构的2:17R'相，与ABCA 3层堆垛周期的2:17R相相比有一层{001}基面原子错排，造成畴壁能密度高于胞内的2:17R相，从而产生不利于方形度的排斥型畴壁钉扎。进一步的对比研究表明，2:17R'相的超晶格衍射斑点可覆盖实验观察到的所有卫星斑，排除了之前文献中根据部分卫星斑所认为的2:17H相或Smn + 1Co5n - 1相。因此，本工作为理解Sm2(Co, M)17磁体方形度低的微结构根源提供了新证据。
陈虹宇 , 宋欣 , 周相龙 , 贾文涛 , 袁涛 , 马天宇 . Sm2Co17磁体胞状组织边缘2:17R'相的透射电子显微镜表征[J]. 金属学报, 2021 , 57(12) : 1637 -1644 . DOI: 10.11900/0412.1961.2020.00412
Pinning-controlled Sm2(Co, M)17 (M = Fe, Cu, and Zr) magnets with cellular nanostructures are the strongest high-temperature permanent magnets. The squareness factor of such magnets is smaller than those of nucleation-controlled permanent magnets, leading to a lower-than-ideal maximum energy product. One of the main reasons for this poor squareness is that the pinning strength is weaker at cell edges than at 1:5H cell boundaries. However, the structure of these edges remains a topic of debate. To identify the microstructure of cell edges, electron diffraction, TEM bright/dark field imaging, and HRTEM imaging on a model magnet Sm25Co50.2Fe16.2Cu5.6Zr3.0 (mass fraction, %) were performed using both [100]2:17R and [101]2:17R zone axes. The results revealed a rhombohedral 2:17R' phase at some of the edges, with one faulting basal layer in the 2:17R lattice. Further comparative investigations revealed that all the extra superlattice reflections result from the 2:17R' phase, excluding the previously identified 2:17H or Smn + 1Co5n - 1 or their mixture that can only produce a part of such superlattice reflections. Owing to the 2:17R' phase with a faulted basal plane, the free energy at the cell edges is higher than that of the 2:17R cell interiors, leading to repulsive domain-wall-pinning unfavorable for the squareness factor. This study provides important evidence for understanding the microstructural origin of the poor squareness factor obtained for Sm2(Co, M)17 permanent magnets.
Key words： permanent magnet; Sm-Co magnet; electron diffraction; defect; TEM characterization
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