Identifications of SmCo5 and Sm+1Co5−1-type phases in 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets

Grain Boundary Evolution of Cellular Nanostructured Sm-Co Permanent Magnets

“…After aging, as shown in Figure 3d,f, the superlattice reflections {011}* and {021}* of 2:17H phase disappeared and there was a disordered rhombohedral phase (2:17R'), producing 1/3 and 2/3 superlattice reflections along the [001]*2:17R and [010]*2:17R directions. Note that the 2:17R' phase had one faulting layer in the 2:17R twins with an ACBA or ABCA basal stacking sequence [23,33,34,42], thus appearing as SFs. The diffuse steaks along [001]*2 :17R showed that there were basal SFs and/or Sm n+1 Co 5n−1 precipitates as Sm n+1 Co 5n−1 precipitates also generate diffuse streaks.…”

“…Within the grain interiors, the 2:17H to 2:17R + 1:5H + 1:3R transformation also evolves the gradual solute partitioning [2,6] where the 2:17R cells are enriched with Fe/Co and depleted in Sm, the 1:5H precipitates are enriched with Sm/Cu and depleted in Fe/Co, and the 1:3R precipitates are enriched with Zr and have an even higher Cu content than the 2:17R phase, e.g., Figure 6 in [20]. Sm n+1 Co 5n−1 precipitates have been frequently observed in solution-treated Fe-rich magnets due to the segregation-related primary precipitation effect, i.e., the local enrichments of Zr and Cu [23][24][25]29,42,43,46]. During the aging process, the decomposition-induced 1:5H and 1:3R precipitates constrained at the grain boundaries are mixed with the Sm n+1 Co 5n−1 primary precipitates.…”

“…However, the magnets usually contain various types of microstructural deficiencies, which weaken the pinning force against DW motions locally and lead to an inhomogeneous demagnetization process as well as a poor squareness factor. These microstructural deficiencies include: (i) the intersections between 1:5H precipitates and the co-existing 1:3R precipitates [14], (ii) the cell edges that usually contain stacking faults (SFs) or the 2:17R' intermediate phase [20], (iii) the defect-aggregated cell boundaries (DACBs) free of the 1:5H phase [21], and (iv) the grain boundaries with sparser 1:5H cell boundary precipitates (i.e., larger cells) than the grain interiors and phase mixture of Zr-stabilized Sm n+1 Co 5n−1 (n = 2, 1:3R; n = 3, 2:7R; n = 4, 5:19R) precipitates that are magnetically softer than the 1:5H precipitates [15,[22][23][24][25][26][27]. Among them, the grain boundaries have been thought to be the primary demagnetization sites [5,28].…”

“…Unlike the first three types of deficiencies that are formed by the decomposition from 1:7H or 2:17H into the phase mixture of the 2:17R/2:17R' phase, 1:5H, and 1:3R precipitates, the formation of the last type-grain boundary deficiencies-is more complex especially for the Fe-rich Sm-Co-Fe-Cu-Zr magnets with a large theoretical (BH) max . Firstly, there is an apparent microstructure difference between the grain boundaries and grain interiors even at the solution-treated state including a higher 2:17R ordering degree, fewer DACBs to be occupied by the 1:5H precipitates during the subsequent aging process, and even Zr-stabilized Sm n+1 Co 5n−1 primary precipitates [23,24,29]. Secondly, the kinetics either for recrystallization or precipitation are distinct between the grain boundaries and grain interiors; the concurrently happening and strongly interacted recrystallization (formation and growth of the nanocells) and precipitation in the Sm-Co magnets make the decomposition kinetics more complex at the grain boundaries during the subsequent aging process.…”

Tip Interface Exchange-Coupling Based on “Bi-Anisotropic” Nanocomposites with Low Rare-Earth Content

“…It has been described like a dream to develop nanocomposite permanent magnets with extremely low rare-earth content. Though neodymium-based and samarium-based alloys dominate the majority of present high-performance permanent magnets, the expensive price and scarcity of rare earth restrict their applications. − Dual phase exchange-coupled nanocomposite magnets are considered as a potential material which can produce advanced permanent magnets and resolve rare earth resource crisis. − Micromagnetic simulation performed by R. Skomski and J. M. D. Coey displayed that a multilayer composed of Sm 2 Fe 17 N 3 and Fe 65 Co 35 can attain an energy product as high as 110–137 MG Oe with a rare-earth content of only 2–7 wt % . To satisfy the effective exchange-coupling requirements, fine control for the size and distribution of the hard and soft phase is necessary so that nanocomposites can retain high magnetizations, large coercivities, and eventually enhanced remanence. − Compared with “top-down” methods, − the “bottom-up” approach has an edge in controlling the size and distribution in the nanocomposites. − To enhance the remanence of the hard phase, several studies have been performed by coupling with high moment soft magnetic nanoparticles (such as Fe, Co). − In our previous work, SmCo 5 nanochips prepared by surfactant-assisted high-energy ball-milling (SAHEBM) were mixed with various soft magnetic nanoparticles to fabricate nanocomposite magnets with high magnetic performance.…”