High resolution scanning electron microscopy study on sintered and cast NdFeB magnets

By using a field-emission gun scanning electron microscope, the microstructural details in sintered and cast NdFeB magnets can be revealed either at high resolution (below 50 nm) or at low magnification (100 X) to view a larger area. In all sintered NdFeB based magnets, many Nd/sub 2/O/sub 3/ particles about 1 mu m in diameter are found. The Nd-rich phase is not limited to the Nd/sub 2/Fe/sub 14/B (2-14-1) grain boundaries; some areas of this phase have dimensions similar to those of the 22 m-14-1 grains. The microstructure of cast NdFeB-based alloys strongly depends on the doping elements. An alloy containing Co and V shows a dendritic Fe-V primary phase with long thin 2-14-1 grains, while an alloy containing Co and Nb shows larger 2-14-1 grains with all phases in the ingot corresponding to phases in the sintered magnets.<>