Grain-boundary structure of explosively compacted Nd-Fe-B magnets

The microstructure of the explosively compacted Nd-Fe-B permanent magnets has been investigated by means of TEM and XRD. It is shown that there are three kinds of phases: matrix Nd2Fe14B, O-rich phases and Nd-rich phase with different structures and compositions in explosively compacted Nd-Fe-B permanent magnets. Matrix Nd2Fe14B is predominantly the hard Nd2Fe14B phase with lattice parameters of a=0.88 nm and c=1.22 nm. The O-rich phase presented at the two-grain boundaries and three-grain junctions, with fcc structures, and lattice parameter is a=0.559 nm. The O-rich phase belong to the compound Nd-Fe-O, and contents of O, Nd and Fe are 56at%, 22at% and 21at%, respectively. It is also shown that a large number of the block-shaped Nd-rich phases are in the two-grain boundary or three-grain junctions or Nd2Fe14B phases, with hcp structure and lattice parameters of a=0.395 nm and c=0.628 nm. The Nd-rich phases belong to compound Nd-O, and contents of Nd and O are 85at% and 12at%, respectively. Also a few dislocations in the boundary phases have been observed.