Influence of 1:7 H phase stability on the evolution of cellular microstructure in Fe-rich Sm-Co-Fe-Cu-Zr magnets

Abstract

Fe-rich Sm2Co17-type magnets have many essential applications prospects in high-temperature operation environments. However, the formation of complete cellular microstructure becomes increasingly difficult when the Fe content of Sm2Co17-type magnets exceeds 20 wt%. Herein, the phase stability of 1:7 H phase and its effect on the precipitation of the 1:5 H precipitates in Fe-rich Sm2Co17-type magnets are investigated. The results confirm that the stability of the 1:7 H phase decreases with the increasing of Fe content for the solution-treated magnets. Not only 2:17 R phase but also a lot of 2:17 R′ phase is found in solution-treated magnets when the Fe content exceeds 22 wt%. As the Fe content increases, the density of initial defects decreases for the growth of 2:17 R nanotwins in the solution-treated magnets. Furthermore, the segregation of Cu in the defects-aggregated cell boundaries weakened gradually. Consequently, the nucleation and precipitation of cell boundary precipitates is difficult, and the cellular microstructure becomes incomplete and coarse when the Fe content is above 22 wt%. The present work may provide a further insight for understanding the evolution of cellular microstructure depending on the phase decomposition behavior in Fe-rich Sm2Co17-type magnets.