Mechanically robust high magnetic-performance Sm-Co sintered magnets through microstructure engineering

Samarium-cobalt (Sm-Co) sintered magnets have high magnetic energy densities, great resistance to demagnetization and corrosion, and excellent thermal stability in a wide temperature range (–50–550 °C). However, the utilization of these magnets is restricted by their brittleness. Based on micromechanical and the Zener pinning model, Sm-Co sintered magnets with improved mechanical properties have been designed and fabricated via microstructure engineering. A small amount of fine Sm2O3 particulates (0–3 wt%) has been incorporated into Sm2(CoFeCuZr)17 sintered magnets to refine the grain size by up to approximately 50% (from 45 to 22 µm) and narrow the grain size distribution. Doping with 3 wt% Sm2O3 increased the flexural strength by 62% while maintaining magnetic performance. Both grain-refined unimodal microstructure and heterogeneous laminated coarse/fine grain microstructure were formed by strategically designed assemblies of Sm2O3-added Sm-Co powder feedstock mixtures. The technology is compatible with existing magnet manufacturing processes. Numerical micromechanics simulation indicates that the fracture is dominated by intragranular mode. The mechanical strength is mainly enhanced by the additive-induced grain refinement, while the small amount of Sm2O3 addition has a small direct positive contribution. These magnets will be more cost-effective, efficient, and robust for various functional applications.This is a manuscript of an article published as Cui, Baozhi, Xubo Liu, Ikenna C. Nlebedim, and Jun Cui. "Mechanically robust high magnetic-performance Sm-Co sintered magnets through microstructure engineering." Journal of Alloys and Compounds 926 (2022): 166869. DOI: 10.1016/j.jallcom.2022.166869. Copyright 2022 Elsevier B.V. Posted with permission. DOE Contract Number(s): AC02-07CH11358

Microstructural evolutions, phase transformations and hard magnetic properties in polycrystalline Ce–Co–Fe–Cu alloys Author links open overlay panel

This work focuses on systematic studies of Ce–Co based 1:5 permanent magnet alloys of CeCo4.4-xFexCu0.6 and CeCo3.9-xFexCu1.2 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.8) by varying Co:Fe. The overarching aim of this manuscript is to elucidate the hard-magnetic properties through a better understanding of phase formation by the structural, microstructural, and magnetic properties in these materials. Improved mutual solubility of Fe in the 1:5 phase has been observed with an extended homogeneity range by Cu substitution. For both composition series, Fe contents of x ≤ 0.6 show a homogeneous microstructure with a single 1:5 phase and good magnetic properties. The composition region 0.6 < x ≤ 0.9 appears to be near the boundary of solubility and evolution of other phases. At x = 1.8, it is found that the homogeneous 1:5 phase and magnetic hardness deteriorated due to the evolution of secondary phases such as 2:17, 2:7, and Fe–Co. The addition of Fe improved both the magnetization and Curie temperature via increased effective exchange interactions, while an increase in Cu content enhanced coercivity.This is a manuscript of an article published as Gandha, Kinjal, Rakesh P. Chaudhary, Matthew J. Kramer, Ryan T. Ott, Durga Paudyal, and I. C. Nlebedim. "Microstructural evolutions, phase transformations and hard magnetic properties in polycrystalline Ce–Co–Fe–Cu alloys." Materials Chemistry and Physics 286 (2022): 126179. DOI: 10.1016/j.matchemphys.2022.126179. Copyright 2022 Elsevier B.V. Posted with permission. DOE Contract Number(s): AC02-07CH11358