Evolution of grain boundary regions in Sm-Co-Fe-Cu-Zr magnets

Grain boundary regions (GBs) with incomplete cellular nanostructure will deteriorate the squareness and coercivity in iron-rich SmCo magnets. In order to reduce the deteriorations, the morphology and evolution of GBs in Sm-Co-Fe-Cu-Zr magnets are systematically investigated. It clearly reveals that less precipitated particles (Zr-rich and Cu-rich particle) disperse in GBs, and more 1:5H cell boundary phase exists from GBs to grain interiors with Cu content increase, which leads to an improvement of squareness. On this basis, the Cu content in 1:5H cell boundary phase is gradually decreases, which partially weakens the coercivity. Our findings suggest that careful controlling Cu content in magnets can effectively optimize the microstructure of grain boundary and promote the cellular nanostructure from GBs to grain interiors. That may provide important considerations for the preparation of magnet with high squareness and high coercivity.