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Vol. 81 (2017) No. 1 p. 2-10




This paper presents our recent microstructure characterization work of Nd-Fe-B sintered magnets with the emphasis of the structure and chemistry of Nd-rich phases at grain boundary triple junctions and thin Nd-rich phases formed along grain boundaries. The use of secondary electron imaging through the in-lens type detector combined with the TEM analysis lead to the unambiguous identification of Nd-rich phases at grain boundary triple junctions. Through microstructure characterization of commercial sintered magnet by the correlative characterization and atomic scale high angle annular dark field scanning TEM (HAADF-STEM)combined with energy dispersive spectroscopy (EDS), we have concluded the formation of non-ferromagnetic grain boundary phase along the grain boundaries parallel to the easy axis is one of the keys to increase the coercivity. The trace addition of Ga into Nd-rich Nd-Fe-B magnet demonstrated the substantial coercivity increase by the formation of non-ferromagnetic Nd-rich grain boundary phase.

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