Identification of 2:17R' Cell Edge Phase in Sm2Co17-Type Permanent Magnets by Transmission Electron Microscopy
CHEN Hongyu1, SONG Xin1, ZHOU Xianglong1, JIA Wentao1, YUAN Tao1,2, MA Tianyu1()
1.Frontier Institute of Science and Technology and State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China 2.The Southwest Applied Magnetism Research Institute, Mianyang 621000, China
Cite this article:
CHEN Hongyu, SONG Xin, ZHOU Xianglong, JIA Wentao, YUAN Tao, MA Tianyu. Identification of 2:17R' Cell Edge Phase in Sm2Co17-Type Permanent Magnets by Transmission Electron Microscopy. Acta Metall Sin, 2021, 57(12): 1637-1644.
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.
Fig.1 TEM bright field images (a, d), dark field images (b, e), selected area electron diffraction (SAED) patterns (c, f) for the Sm25Co50.2Fe16.2Cu5.6Zr3.0 magnet taken along [100]2:17R (a-c) and [101]2:17R (d-f) zone axes (The dark field images were taken using the (010)2:17R' or (020)2:17R' superlattice reflections circled by white in Figs.1c and f)
Fig.2 HRTEM characterizations of Sm25Co50.2Fe16.2Cu5.6Zr3.0 magnet along [100]2:17R (a-c) and [101]2:17R (d-i) zone axes (Sm positions are indicated by white circles)(a-c) HRTEM image, fast Fourier transform (FFT) pattern, and inverse fast Fourier transform (IFFT) image of the cell edge, respectively (d-f) HRTEM image, FFT pattern, and IFFT image of the 2:17R cell interior, respectively (g-i) HRTEM image, FFT pattern, and IFFT image of the 2:17R' cell edge, respectively
Fig.3 Simulated electron diffraction patterns for 2:17H (a1, b1), 1:5H (a2, b2), 1:3R (a3, b3), 2:7R (a4, b4), and 5:19R (a5, b5) phases along their specific zone axes parallel to [100]2:17R (a1-a5) and [101]2:17R (b1-b5)
Fig.4 TEM bright field images of Sm25Co42.9Fe23.5Cu5.6Zr3.0 magnet along [100]2:17R at grain interior (a) and grain boundary (GB) (d) regions, FFT pattern (b) and IFFT image (c) of the grain interior 1:3R platelet, and FFT pattern (e) and IFFT image (f) of the grain boundary 2:7R
Fig.5 Unit cells (a1, a2), projections (b1, d1, b2, d2), and simulated electron diffraction patterns (c1, e1, c2, e2) along [100]2:17R and [101]2:17R zone axes of 2:17R (a1-e1) and 2:17R' (a2-e2)
Fig.6 Updated schematic domain wall energy density profile across 1:5H cell boundary (CB), 2:17R' cell edge, and 2:17R cell interior (“Attractive” refers to the attractive domain-wall-pinning, “repulsive” refers to the repulsive domain-wall-pinning)
1
Ojima T, Tomizawa S, Yoneyama T, et al. Magnetic properties of a new type of rare-earth cobalt magnets Sm2(Co, Cu, Fe, M)17 [J]. IEEE Trans. Magn., 1977, 13: 1317
2
Buschow K H J. New developments in hard magnetic materials [J]. Rep. Prog. Phys., 1991, 54: 1123
3
Zhu M G, Sun W, Fang Y K, et al. The research progress and status of Sm-Co permanent magnet materials [J]. Mater. China, 2015, 34: 789
Liu J P, Fullerton E, Gutfleisch O, et al. Nanoscale Magnetic Materials and Applications [M]. New York: Springer, 2009: 337
5
Coey J M D. Permanent magnets: Plugging the gap [J]. Scr. Mater., 2012, 67: 524
6
Strnat K J. The hard-magnetic properties of rare earth-transition metal alloys [J]. IEEE Trans. Magn., 1972, 8: 511
7
Horiuchi Y, Hagiwara M, Endo M, et al. Influence of intermediate-heat treatment on the structure and magnetic properties of iron-rich Sm(Co, Fe, Cu, Zr)z sintered magnets [J]. J. Appl. Phys., 2015, 117: 17C704
8
Goll D, Kronmüller H, Stadelmaier H H. Micromagnetism and the microstructure of high-temperature permanent magnets [J]. J. Appl. Phys., 2004, 96: 6534
9
Skomski R. Domain-wall curvature and coercivity in pinning type Sm-Co magnets [J]. J. Appl. Phys., 1997, 81: 5627
10
Katter M, Weber J, Assmus W, et al. A new model for the coercivity mechanism of Sm2(Co, Fe, Cu, Zr)17 magnets [J]. IEEE Trans. Magn., 1996, 32: 4815
11
Kronmüller H, Goll D. Micromagnetic analysis of pinning-hardened nanostructured, nanocrystalline Sm2Co17 based alloys [J]. Scr. Mater., 2002, 47: 545
12
Gong S T, Jiang C B, Zhang T L. Effect of Fe on microstructure and coercivity of SmCo-based magnets [J]. Acta Metall. Sin., 2017, 53: 726
Xiong X Y, Ohkubo T, Koyama T, et al. The microstructure of sintered Sm(Co0.72Fe0.20Cu0.055Zr0.025)7.5 permanent magnet studied by atom probe [J]. Acta Mater., 2004, 52: 737
14
Xia W, He Y K, Huang H B, et al. Initial irreversible losses and enhanced high-temperature performance of rare-earth permanent magnets [J]. Adv. Funct. Mater., 2019, 29: 1900690
15
Xu C, Wang H, Zhang T L, et al. Correlation of microstructure and magnetic properties in Sm(CobalFe0.1Cu0.1Zr0.033)6.93 magnets solution-treated at different temperatures [J]. Rare Met., 2019, 38: 20
16
Guo Z H, Li W. Room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x = 0-0.30) sintered magnets [J]. Acta Metall. Sin., 2002, 38: 866
Machida H, Fujiwara T, Kamada R, et al. The high squareness Sm-Co magnet having Hcb = 10.6 kOe at 150oC [J]. AIP Adv., 2017, 7: 056223
18
Zhou X L, Song X, Jia W T, et al. Identifications of SmCo5 and Smn + 1Co5n - 1-type phases in 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets [J]. Scr. Mater., 2020, 182: 1
19
Wang Y Q, Yue M, Wu D, et al. Microstructure modification induced giant coercivity enhancement in Sm(CoFeCuZr)z permanent magnets [J]. Scr. Mater., 2018, 146: 231
20
Yan G H, Xia W X, Liu Z, et al. Effect of grain boundary on magnetization behaviors in 2:17 type SmCo magnet [J]. J. Magn. Magn. Mater., 2019, 489: 165459
21
Rabenberg L, Mishra R K, Thomas G. Microstructures of precipitation-hardened SmCo permanent magnets [J]. J. Appl. Phys., 1982, 53: 2389
22
Duerrschnabel M, Yi M, Uestuener K, et al. Atomic structure and domain wall pinning in samarium-cobalt-based permanent magnets [J]. Nat. Commun., 2017, 8: 54
23
Horiuchi Y, Hagiwara M, Okamoto K, et al. Effect of pre-aging treatment on the microstructure and magnetic properties of Sm(Co, Fe, Cu, Zr)7.8 sintered magnets [J]. Mater. Trans., 2014, 55: 482
24
Fidler J, Skalicky P, Rothwarf F. High resolution electron microscope study of Sm(Co, Fe, Cu, Zr)7.5 magnets [J]. IEEE Trans. Magn., 1983, 19: 2041
25
Maury C, Rabenberg L, Allibert C H. Genesis of the cell microstructure in the Sm(Co, Fe, Cu, Zr) permanent magnets with 2:17 type [J]. Phys. Status. Solidi, 1993, 140A: 57
26
Feng H B, Chen H S, Guo Z H, et al. Twinning structure in Sm(Co, Fe, Cu, Zr)z permanent magnet [J]. Intermetallics, 2010, 18: 1067
27
Delannay F, Derkaoui S, Allibert C H. The influence of zirconium on Sm(CoFeCuZr)7.2 alloys for permanent magnets I: Identification of the phases by transmission electron microscopy [J]. J. Less-Common. Met., 1987, 134: 249
28
Xu C, Wang H, Liu B J, et al. The formation mechanism of 1:5H phase in Sm(Co, Fe, Cu, Zr)z melt-spun ribbons with high iron content [J]. J. Magn. Magn. Mater., 2020, 496: 165939
29
Song X, Zhou X L, Yuan T, et al. Role of nanoscale interfacial defects on magnetic properties of the 2:17-type Sm-Co permanent magnets [J]. J. Alloys Compd., 2020, 816: 152620
30
Jia W T, Zhou X L, Xiao A D, et al. Defects-aggregated cell boundaries induced domain wall curvature change in Fe-rich Sm-Co-Fe-Cu-Zr permanent magnets [J]. J. Mater. Sci., 2020, 55: 13258
31
Song X, Ma T Y, Zhou X L, et al. Atomic scale understanding of the defects process in concurrent recrystallization and precipitation of Sm-Co-Fe-Cu-Zr alloys [J]. Acta Mater., 2021, 202: 290
32
Song X, Liu Y, Xiao A D, et al. Cell-boundary-structure controlled magnetic-domain-wall-pinning in 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets [J]. Mater. Charact., 2020, 169: 110575
33
Rabenberg L, Mishra R, Thomas G. Development of the cellular microstructure in the SmCo7.4-type magnets [A]. The Proceeding 6th International Workshop on Rare Earth-Cobalt Permanent Magnets and Their Applications [C]. Australia: JOSEF FIDLER, Druckerei Lischkar & Co A-1120 Vienna, 1982: 599
34
Chen H S, Wang Y Q, Yao Y, et al. Attractive-domain-wall-pinning controlled Sm-Co magnets overcome the coercivity-remanence trade-off [J]. Acta Mater., 2019, 164: 196
35
Tian Y, Liu Z, Xu H, et al. In situ observation of domain wall pinning in Sm(Co, Fe, Cu, Zr)z magnet by Lorentz microscopy [J]. IEEE Trans. Magn., 2015, 51: 2102404
