Elements Strategy Initiative Center for Magnetic Materials (ESICMM),
National Institute for Materials Science (NIMS), Tsukuba, Japan
Abstract:
Due to the recent concern about the stable supply of heavy rare earth elements (HRE), finding a way to increase the coercivity of Nd-Fe-B magnets without Dy has become the center of permanent magnet research in Japan. In this talk, we will update our recent progress toward the development of high coercivity Nd-Fe-B permanent magnets. To obtain complete understanding of the microstructure-coercivity relationships, we revisited the microstructures of Nd-Fe-B sintered and hot-deformed magnets using aberration-corrected STEM complemented by atom probe tomography (APT). In addition, we employed electron backscatter diffraction to determine the misorientation of the grain boundaries. We found that the structure and chemical composition of the grain boundary phase show strong orientation dependence, i.e., the grain boundary phase parallel to the c-planes are mostly crystalline with a higher Nd concentration in contrast to that lying parallel to the c-axis that contains higher Fe content with the amorphous structure. These investigations have suggested it is the key to decouple intergrain exchange decoupling along c-planes of anisotropy magnets. We discuss the way to achieve coercivity higher than 2.5 T based on these new results.
This work was supported by JST, CREST.
This work was supported by JST, CREST.
Fig. 1. Two types of grain boundary phase in a commercial Nd-Fe-B sintered magnet.