Effects of 1:5H-type Cu-rich phase around grain boundary on cell boundary phase and squareness of the demagnetization curve in sintered Sm2Co17-type magnets

The unique cellular structure of Sm2Co17-type magnets is responsible for their outstanding magnetic properties. However, the cell boundary phase around grain boundaries is few, and cannot form a complete cellular structure. This study explores the microstructure and microchemistry of the grain interiors and grain boundary regions in both the solid solution precursor and the final magnet. The Cu-rich phase precipitates around grain boundaries in the solid solution precursor, and it remains present in the final magnet. The Cu-rich phase is not present as a standalone grain boundary phase, rather, it possesses a hexagonal CaCu5-type crystal structure and demonstrates a coherent orientation relationship with the surrounding matrix. The Cu-rich phase inhibits cellular structure formation nearby, while boosting Cu content in the cell boundary phase at the grain boundary regions in the final magnet. The formation of a Cu-rich phase around the grain boundary increases the heterogeneity of the domain wall pinning field in the final magnet, becoming an unfavorable factor for the improvement of the squareness of the demagnetization curve. These discoveries enhance our comprehension of the precipitated phase surrounding the grain boundary and its impact on the cellular structure and magnetic characteristics of the magnet.