Phase Transformation at High Temperatures and Coercivity of Sm-Co-Cu-Fe Magnet Alloys

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  • Morita Yoshio
    Department of Metallurgy, Faculty of Engineering, The University of Tokyo
  • Umeda Takateru
    Department of Metallurgy, Faculty of Engineering, The University of Tokyo
  • Kimura Yasuo
    Faculty of Engineering, The University of Tokyo

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  • Sm-Co-Cu-Fe系磁石合金の高温における相変態と保磁力について
  • Sm Co Cu Feケイ ジシャク ゴウキン ノ コウオン ニ

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It is well known that Sm(Co,Cu,Fe)z (Z=near 7) alloys containing a proper quantity of Cu and Fe possess high coercivity and are used as superior permanent magnet materials. The Sm-Co-Cu-Fe quaternary phase diagram has not been studied. Therefore, the phase diagram near compositions of magnet alloys, and furthermore, relationships between phase transformations at high temperatures and coercivities were investigated. That is, Sm-Co-13 at%Cu-10 at%Fe and Sm-Co-9 at%Cu-18 at%Fe sections of the phase diagram were determined in the Sm content range from 10 to 15 at%. Furthermore, for various Sm(Co,Cu,Fe)z (Z=near 7) alloys, relationships between crystal structures after homogenizing treatment and coercivities after aging treatment were examined. The results are summarized as follows:<BR>(1) The Sm2(Co,Cu,Fe)17 intermetallic compound (2/17 phase) has solubility from 10.5 to about 13.0 at%Sm at high temperatures. In the extended homogeneity region, the 2/17 phase possesses the hexagonal TbCu7 structure or the rhombohedral Th2Zn17 structure depending on the quantity of Cu and Fe. The limits of the former compositions are given by approximately 16≤Cu(at%)+0.73Fe(at%)≤23 and Cu(at%)+3>Fe(at%).<BR>(2) The Sm(Co,Cu,Fe)z (Z=near 7) alloys quenched after homogenizing treatment, by which the 2/17 phase with TbCu7 structure is obtained, can possess high coercivity after the aging treatment.

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