Microstrucutre of HRE Grain Boundary Diffusion Processed Nd-Fe-B Sintered Magnets

Recently, the grain boundary diffusion processing (GBDP) using heavy rare earth elements(HRE) such as Dy and Tb has evolved as an efficient method to enhance the coercivity ofNd-Fe-B sintered magnets without significant loss in remanence. In this work, Dy-enrichedcore/shell structure of GBDP Nd-Fe-B magnet is studied in detail. We found the shellssurrounding faceted Nd2Fe14B grains are generally asymmetric along GB. The shellstructure with the faceted core is characterized by SEM/EBSD and TEM. The orientations ofthe Nd2Fe14B grains were determined by EBSD, thereby faceting planes were identified tobe {100}, {101} and {410} planes. Also the chemical composition at the core/shellinterface as well as the grain boundaries were measured by SETEM/EDS. Based on themicrostructural features and thermodynamic calculations, mechanism of the shell structureformation and its contribution to the coercivity are discussed.