Influence of misch metal content on microstructure and magnetic properties of R–Fe–B magnets sintered by dual alloy method

Abstract

MM 14 Fe 79.9 B 6.1 /Nd 13.5 Fe 80.5 B 6 magnets were fabricated by dual alloy method (MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures T c1 corresponds to the main phase which contains more LaCe, and T c1 decreases from 276.5 • C to 256.6 • C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of B r with the increase of MM indicates the existence of inter-grain exchange coupling in the magnets. When MM/R ≤ 30.3 at.%, the magnetic properties can reach the level of the intrinsic coercivity H cj ≥ 7.11 kOe and the maximum energy product (BH) max ≥ 41 MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process, and this will cause the decrease of H cj . Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.

High performance RE–Fe–B sintered magnets with high-content misch metal by double main phase process

“…The sharp decrease of (BH) max from 382.5 kJ/m 3 to 95.70 kJ/m 3 and the remarkable diminishment of H cj from 1219 kA/m to 111.8 kA/m are observed with increasing MM substitution from x = 0.0 to 1.0. The magnetic performance of x = 1.0 magnets is better than those reported in the literatures, [20,22,[25][26][27] as illustrated in Fig. 2.…”

“…Figure 2 shows the comparison of (BH) max of [(Pr, Nd) 1−x MM x ] 13.8 Fe bal M 1.5 B 5.9 (x = 0.0, 0.5, 0.7, and 1.0) magnets with those of some MM based sintered magnets reported in the literatures. [20,22,[25][26][27][28][29] Generally, a dramatic drop of (BH) max occurs when x exceeds 0.5 for all the sintered magnets except the one fabricated by DMP process in this work. It is worthy to note, as mentioned previously, that the sintered magnets of x = 1.0, i.e., MM 13.8 Fe bal M 1.5 B 5.9 magnets in this work show the highest (BH) max to date, it is reasonable to conclude that the excellent magnetic performances of the sintered magnets by DMP process in this work probably could be attributed to the superior magnetic properties of the original alloy of MM 13.8 Fe bal M 1.5 B 5.9 .…”

“…[24] By DMP method, when MM/RE = 30.3 at.%, the sintered RE-Fe-B magnets have H cj = 566 kA/m and (BH) max = 326 kJ/m 3 . [22] However, in the MM-based sintered magnets prepared by DMP process, there is no significant enhancement of coercivity as observed in Ce-based sintered magnets fabricated by the same process. And the RE-Fe-B magnetic material with La, Ce, or MM content higher than 50 at.% is rarely investigated so far, the amount of La, Ce, or MM substitution for Nd in RE-Fe-B magnets is usually below 50 at.% in the previous research.…”

“…In addition, due to the relatively lower intrinsic magnetic properties of La 2 Fe 14 B (saturation magnetization µ 0 M s = 1.38 T, magnetocrystalline field H A = 2069 kA/m, and Curie temperature T c = 530 K) and Ce 2 Fe 14 B (µ 0 M s = 1.17 T, H A = 1592 kA/m, and T c = 424 K) compared to Nd 2 Fe 14 B (µ 0 M s = 1.60 T, H A = 5809 kA/m, and T c = 585 K), [15,16] the magnetic properties of La, Ce, or MM doping single main phase (SMP) RE-Fe-B magnets deteriorate rapidly with increasing La, Ce, or MM content. [12,17,18] Recently, a novel process known as double main phase (DMP) process has been proposed [3,[19][20][21][22][23] to fabricate RE-Fe-B sintered magnets by blending two kinds of powders of different compositions, such as Pr-Nd-Fe-B and La, Ce, or MM based RE-Fe-B, respectively. As a result, the remanence B r = 1.240 T, the intrinsic coercivity H cj = 716.2 kA/m, and the maximum magnetic energy product (BH) max = 292.0 kJ/m 3 can be obtained at a high Ce substitution level of 45 wt.%.…”

Magnetic properties of misch-metal partially substituted Nd–Fe–B magnets sintered by dual alloy method

“…[1,2] In order to reduce the production costs more rationally and make rational use of rare earth resources, the partial substitution of misch-metal (MM) for Nd in Nd-Fe-B sintered magnets is thought to be an effective method to pursue high cost performance because of the inferior intrinsic properties and low cost of MM 2 Fe 14 B. [3][4][5][6] It has been found that the magnetic properties deteriorate drastically when Nd is replaced by Ce/La homogeneously in the 2:14:1 phase lattice. [5] Compared with the traditional single alloy method, the dual alloy method by mixing MM 2 Fe 14 B with Nd 2 Fe 14 B powders has an obvious advantage in preparing high abundant rare earth permanent magnets.…”