Permanent magnet alloys based on Sm₂Co₁₇; phase evolution in the quinary system Sm–Zr–Fe–Co–Cu

Abstract

In the five-component permanent magnets based on Sm 2 Co 17 the formation of the familiar microstructural features (2 : 17 cell, 1 : 5 cell wall, and 1 : 3 lamellae) are elucidated with the help of recent and past information on the phase equilibria and crystal structures. Contrary to Zr-free alloys, in which the 1 : 5 cell-wall phase can form directly, the quinary alloys, to attain peak magnetic coercivity, undergo a transformation within the cell walls from undesirable 2 : 7 + 5 : 19 to high-anisotropy 1 : 5. A dramatic increase in the Cu content of the cell wall accompanies this transformation.

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

“…It was proposed [12] that the coercivity mechanism in these magnets is related to the pinning of domain walls at the 1:5 boundary phase. Several recent studies attribute coercivity to a combination of pinning and nucleation mechanisms [5,13,14]. More specifically, it has been confirmed by several authors [13,14] that the angu- [2].…”

“…The effect of Zr remains somewhat controversial: recently, Stadelmaier et al [5] have suggested that the function of the Zr would be to improve a possible "imperfect shape" of the cell walls and thereby increase coercivity. 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.…”

“…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].…”

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)Z Permanent Magnets: First Level of Heterogeneity

“…Currently, it is obvious that during heat treatment for the high-coercivity state, at the end of the solid solution heat treatment (SSHT), the starting matrix, in the classical sense of this term, is formed based on the disordered 1:7H phase [ 3 , 4 , 5 , 6 ] (from herein, the designation of A n B m intermetallics is given in the form of n:mH or n:mR, where H and R indicate the hexagonal and rhombohedral crystal lattices, respectively).…”

“…Despite numerous investigations into the structural formation and properties of the alloys, the studies are far from over. The phase transformations, which occur during stepped tempering, and the transformations that cause the instant “recovery of properties” upon repeated heating of samples to the isothermal tempering temperature being among them [ 3 , 4 ], have not yet been described. The phase composition of boundaries between cells at different states of heat treatments [ 3 , 4 , 5 , 6 ] meets with strongly conflicting views.…”