Precipitation in NdFeB-type magnet materials

The microstructure of sintered magnets and melt-spun samples made from Nb-containing (Nd,Dy)FeB material has been investigated using transmission and scanning electron microscopy, X-ray microanalysis and thermogravimetric analysis. Comparison of the sintered specimens with NdDyFeB and NdFeB magnets revealed the existence of two additional phases. One of these is an Fe
2
Nb Laves compound. The second additional phase takes the form of small Nb-containing coherent precipitates within the main Nd
2
Fe
14
B grains. In the sintered magnet these particles ranged in size from 20-50 nm. Melt-spun ribbon contained a dispersion of smaller inclusions, typically 5-10 nm in diameter. The presence of these precipitates may be related to the enhanced coercivity found in the magnet and melt-spun samples.