Co corner of the system SmCoZr: decomposition of the phase 1:7 and equilibria at 850°C

Impurity phases in Sm(CoFeCuZr)z magnets: The role of Zr

“…If they were not present, probably the alloy would be monophase, as its mean composition is very close to that of the lighter phase, assumed to be 1:7. Coherently, this alloy is located within the 1:7 phase field according to the Sm-Co-Zr diagram presented by Derkaoui et al [17] and Lefevre et al [18,19]. According to these authors, compositions in this phase field have a single phase at elevated temperatures, a necessary condition for obtaining the required microstructure of high coercivity magnets.…”

“…Ojima et al [16] found that small amounts of Zr permitted the Fe content of 2:17 magnets to be increased without Co-Fe precipitation. The important role of Zr in stabilizing the high-temperature phase has been emphasized by Derkaoui et al [17] and Lefevre et al [18,19]. Popov et al [20] and Huang et al [21] have also confirmed that Zr stabilizes the high-temperature phase.…”

“…Nevertheless, it should be pointed out that Zr addition increases the 1:7 field at high temperature [17][18][19] and naturally will favor the process that gives origin to the ideal cellular nanostructure. Hadjipanayis [26] reported that increasing the Zr content leads to an increase of the cell size, and this moves the cell size near to D c -the critical domain size of 2:17 phase, which is beneficial for coercivity.…”

“…The remarkable characteristics of permanent magnets based on Sm 2 (CoFeCuZr) 17 , such as high intrinsic coercivities at high temperatures (µ 0i H c up to 1 T at 500 • C [1,2]), maintain them as subjects of considerable interest and study [3][4][5][6]. Furthermore, SmCo magnets remain the choice material for a number of applications, such as travelling wave tubes for radar systems [7,8].…”

Behavior of residual carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets

“…The Cu enrichment at the cell boundaries led to a higher domain wall energy gradient and thus to a higher coercivity. Besides, the investigations by Derkaoui et al [19,20] pointed out that the addition Zr could stabilize TbCu 7 -type 1:7 phase with the composition range of the alloy from SmCo 5 to Sm 2 Co 17 at 1150 • C. The 1:7 phase decomposed into 2:17 and 1:5 phases when the temperature varied from 1150 • C to 850 • C. After aging at 850 • C, the microstructure of Sm 10.5 Co 87.5 Zr 2 alloy had a lamella phase, which was parallel to the matrix phase. Therefore, Zr can promote the formation of the cellular microstructure of Sm(Co, Fe, Cu, Zr) z magnets and provide condition for excellent magnetic properties.…”