HIGH-RESOLUTION ELECTRON-MICROSCOPE STUDY OF THE GRAIN-BOUNDARY PHASE IN RAPIDLY QUENCHED ND-FE-B PERMANENT-MAGNET ALLOYS

The grain boundary phase in rapidly quenched Nd-Fe-B magnets has been characterized by high-resolution transmission electron microscopy. The grain boundary phase structure is the same in both isotropic and oriented magnets; it is ordered face-centered cubic with a lattice parameter of 5.58 angstrom. The composition of this phase has not been determined directly, but is most likely a Nd/Fe ratio of 3, with possibly some interstitial B. In both isotropic and oriented magnets, some grain boundaries are completely free of any second phase, and when the grain boundary phase is present, its thickness is highly variable.