種々の希土類化合物を用いて粒界拡散処理したNd-Fe-B系焼結磁石の保磁力

抄録

In order to clarify the origin of coercivity enhancement of Nd-Fe-B sintered magnets by the Grain BoundaryDiffusion Process (GBDP), microstructural observations were performed and the coercivities of magnets processed with various rare-earth oxides were investigated. Microstructural analysis using FE-EPMA revealed that Dy supplied from the magnet surface diffused into whole magnets with a thickness of 2 mm. At the center of a magnet, the Dy distribution width around a grain boundary is almost comparable to the width of the Nd-rich grain boundary phase.When rare-earth (R) oxides whose R provide higher anisotropy in R₂Fe₁₄B than that of Nd₂Fe₁₄B, are used for GBDP, the magnets showed higher coercivity than that of the control, and vice versa. Although the diffusion depth of Dy into the Nd₂Fe₁₄B grains was unclear at the center of the magnet, the relationship between the kinds of rare-earth elements used for GBDP and the resultant coercivities strongly suggests that the rare-earth elements supplied from the surface of the magnets and absorbed along the grain boundary phase may diffuse into very thin portions of the Nd₂Fe₁₄B grain surface.