Microstructure of Explosively Compacted Nd-Fe-B Magnets

The microstructure of explosively compacted Nd-Fe-B alloys has been investigated by means of transmission electron microscopy and X-ray diffraction. It is shown that there are three kinds of phases, i.e. the matrix phase Nd2Fe14B, O-rich phases and Nd-rich phases in explosively compacted Nd-Fe-B magnets. The matrix Nd2Fe14B phase is tetragonal, with lattice parameters of a=0.88 nm and c=1.22 nm. The O-rich phase was present at the two-grain boundary and three-grain junctions, with the fcc structure, and the lattice parameter is a=0.559 nm. The O-rich phase belongs to the compound Nd-Fe-O, and the contents of O, Nd and Fe are 45–60 at%, 20–40 at% and 10–21 at%, respectively. It is also shown that a large number of block-shaped Nd-rich phases are in a two-grain boundary or three-grain junctions or Nd2Fe14B phase, with the hcp structure and the lattice parameters of a=0.395 nm and c=0.628 nm. The Nd-rich phases belong to compound Nd-O, and the contents of Nd and O are 80–85 at% and 10–15 at%, respectively. Also a few dislocations in the boundary phase have been observed.