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. 2024 Jun 25;17(13):3110.
doi: 10.3390/ma17133110.

Exploring Sintered Fe-(Ce, Nd)-B with High Degree of Cerium Substitution as Potential Gap Magnet

Dagmar Goll  1 , Ralf Loeffler  1 , Marius Boettle  1 , Joerg Buschbeck  2 , Gerhard Schneider  1
Affiliations

Exploring Sintered Fe-(Ce, Nd)-B with High Degree of Cerium Substitution as Potential Gap Magnet

Dagmar Goll et al. Materials (Basel). .

Abstract

The more effective use of readily available Ce in FeNdB sintered magnets is an important step towards more resource-efficient, sustainable, and cost-effective permanent magnets. These magnets have the potential to bridge the gap between high-performance FeNdB and hard ferrite magnets. However, for higher degrees of cerium substitution (>25%), the magnetic properties deteriorate due to the lower intrinsic magnetic properties of Fe14Ce2B and the formation of the Laves phase Fe2Ce in the grain boundaries. In this paper, sintered magnets with the composition Fe70.9-(CexNd1-x)18.8-B5.8-M4.5 (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal; x = 0.5 and 0.75) were fabricated and analyzed. It was possible to obtain coercive fields for higher degrees of Ce substitution, which previous commercially available magnets have only shown for significantly lower degrees of Ce substitution. For x = 0.5, coercivity, remanence, and maximum energy product of µ0Hc = 1.29 T (Hc = 1026 kA/m), Jr = 1.02 T, and (BH)max = 176.5 kJ/m3 were achieved at room temperature for x = 0.75 µ0Hc = 0.72 T (Hc = 573 kA/m), Jr = 0.80 T, and (BH)max = 114.5 kJ/m3, respectively.

Keywords: Ce substitution; Ce2Fe14B; Nd2Fe14B; NdFeB; cerium; coercivity; permanent magnet; rare-earth-based magnet; sintered magnet.

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Conflict of interest statement

Author Joerg Buschbeck is employed by the company Siemens AG. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Flow chart of the synthesis procedure (including processing conditions) and analysis methods used.
Figure 2
Figure 2
Particle size distributions using laser diffraction of the powders used for fabrication of the Ce0.5 and Ce0.75 sintered magnets. The values of d10, d50, and d90 are also listed.
Figure 3
Figure 3
Differential scanning calorimetry (DSC) analysis performed on the Ce0.5 and Ce0.75 sintered magnets, heated from 25 °C to 1300 °C and 1200 °C with 10 °C/min, respectively. In the temperature range (T1, T2), partial melting occurs, while at (T3), the 14:2:1 phase is fully liquid. Sintering temperatures are labelled (Tsin). The measurement curve for Ce0 is also shown. Here, partial melting starts at temperatures of approximately 550 °C.
Figure 4
Figure 4
Hysteresis loops of Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5) and Fe70.9-(Ce0.75Nd0.25)18.8-B5.8-M4.5 (Ce0.75) (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal) sintered magnets at RT (20 °C) and 100 °C. Additionally, the RT curve of the Ce0 sintered magnet is shown in the second quadrant (dashed line, measurement performed in hysteresis graph after saturation at 7 T).
Figure 5
Figure 5
J-T kinkpoint measurements of Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5) and Fe70.9-(Ce0.75Nd0.25)18.8-B5.8-M4.5 (Ce0.75) (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal) sintered magnets. The Curie temperature TC is derived from the turning point of the curves. The Curie temperature of Fe14Nd2B of 312 °C is also shown.
Figure 6
Figure 6
Correlative optical microscopy (a) with SEM-BSE and SEM-EDS analysis (b) used to identify the phases shown for sample Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5). Measured mean composition (at%) for 14:2:1 (ϕ-phase) was Fe78.2Nd7.4Ce5.4Mbal and for Fe2RE Fe59.1Nd6.3Ce27.3Mbal.
Figure 7
Figure 7
Quantitative analysis of phase content in Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5) and Fe70.9-(Ce0.75Nd0.25)18.8-B5.8-M4.5 (Ce0.75) (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal) sintered magnets. Light optical micrographs of representative bright-field views (a,b) with corresponding false color representation of detected phases (c,d).
Figure 8
Figure 8
Summary of phase fractions from quantitative microstructure analysis of samples Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5) and Fe70.9-(Ce0.75Nd0.25)18.8-B5.8-M4.5 (Ce0.75) (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal).
Figure 9
Figure 9
Quantitative SEM-EBSD analysis of degree of magnetic texturing (a,c) and grain size (b,d) of samples Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5) and Fe70.9-(Ce0.75Nd0.25)18.8-B5.8-M4.5 (Ce0.75) (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal).
Figure 10
Figure 10
B-H-demagnetization curve in the second quadrant between the remanence Br and the coercivity HcB in the temperature range 20–100 °C for sample Fe70.9-(Ce0.5Nd0.5)18.8-B5.8-M4.5 (Ce0.5) (M = Co, Ti, Al, Ga, and Cu; with Ti, Al, Ga, and Cu less than 2.0 at% in total and Cobal). Linearity is important for the application in electrical machines.
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