The microstructural features of sintered NdFeB magnets have crucial influence on their magnetic performance. To improve the magnetic properties, the knowledge of the relationship between microstructure and functional properties is extensively investigated.
The typical microstructure of NdFeB magnets features grains of Nd2Fe14B phase surrounded by a thin Nd-rich grain boundary layer and Nd-rich phases at the triple junctions. Identification of these phases by electron microscopy methods is rather difficult because these secondary phases show a high tendency to oxidize during sample preparation for electron microscopy analysis.
SEM micrographs of polished cross-section of NdFeB magnet at different magnifications.
TEM micrographs showing thin intergranular phases and secondary triple grain boundary phases.