Recent Progress on Phase Transformations of 2∶17-type Sm-Co Permanent Magnets

The second-generation rare-earth (RE) permanent magnets (PMs), 2: 17-type Sm-Co-Fe-Cu-Zr magnets, are the strongest high-temperature PMs, which have wide applications in advanced industries. However, the fundamental interest in REPMs was moved from 2:17-type magnets to the third-generation Nd-Fe-B magnets in 1980s, leaving some fundamental questions unsettled. One of the fundamental issues is the long-standing dispute on phase decomposition mechanism, which cannot provide clear guidance to develop high-performance 2:17-type magnets. With the advanced techniques, such as in-situ high-energy synchrotron X-ray diffraction (HES-XRD) and Cs-HRTEM, the detailed decomposition process of supersaturated solid solutions into multi-phase coexisting cellular nanostructure has clearly been revealed, clarifying this dispute. In this short review, the latest advances in solid-state phase transformation mechanism, defects formation and dissociation processes, correlation between defects and magnetic properties, and defects-control oriented fabrication methods of 2: 17-type Sm-Co-Fe-Cu-Zr magnets were briefly reviewed. We hope that this review article can be helpful for the community, from the understanding of fundamental contributions to the future development of high-performance magnets. © 2023 Cailiao Daobaoshe/ Materials Review. All rights reserved.