Microstructure of Nd-Rich Grain Boundary Phase in Die-Upset Nd-Fe-Co-Ga-B Magnet

Microstructure of die-upset Nd-Fe-Co-Ga-B magnet was investigated with a scanning electron microscopy (SEM), high resolution and analytical transmission electron microscopy (HRTEM and ATEM). Inside the original melt-spun flakes in the magnet, the typical texture consists of fine platelet Nd2(Fe,Co)14B grains surrounded continuously by a thin grain boundary (GB) phase with 2–3 nm in thickness. The GB phase has an amorphous structure of which the chemical composition is Nd44Fe39Co10Ga7. It was found that high fluidity of the Ndand Ga-rich GB phase contributes to produce a high crystallographic c-axis alignment of Nd2(Fe,Co)14B grains. Near the interfaces of the original flakes, morphology of the Nd2(Fe,Co)14B grains changes from platelet to globular involving the deterioration of c-axis alignment. Many Nd-oxide (NdO and fcc-(Nd,Fe)Ox) grains and a large amount of fine Nd3Co precipitates are formed near the interfaces, and then the composition of GB phase changes to Nd36Fe50Co9Ga5. The insufficiency of Nd in the GB phase and the existence of Nd-oxide particles prevent the anisotropic growth of Nd2(Fe,Co)14B grains, and then lead to the inhomogeneous GB phase and the low c-axis alignment. [doi:10.2320/matertrans.M2011180]

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