Microstructure of Alpha-Fe/NdFeB Type Nanocomposite Magnets

摘要

The microstructure of amorphous-phase remaining alpha-Fe/NdFeB nanocomposite Nd_vFe_balCo_8Nb_xCu_yB_z (v=6-8, x=0-2.5, y=0-0.5 and z=6-7 at percent) magnet alloys, which were prepared by melt spinning, was investigated by means of high resolution transmission electron microscopy (HR-TEM), three-dimensional atom probing (3DAP), and Moessbauer spectroscopy. It is found by HR-TEM that a small amount of amorphous phase remains in the intergranular region between crystal grains of alpha-Fe and Nd_2Fe_14B_1 even after heat treatment at 740 deg.C. The results of 3DAP showed that Nb and B atoms are significantly enriched in the remaining amorphous phase. Moessbauer spectroscopy revealed that the intergranular region is composed of not only so called amorphous phase but also several thin layered phases which have a rather strong hyperfine field distinctively, and that the volume fractions of both the total intergranular phases and the Nd_2Fe_14B_1 phase increase with increasing Nb content. The coercivity-enhancing effect of Nb addition is discussed on the basis of the above experimental result.