A study on the c-axis alignment of Nd-Fe-B die-upset magnets (abstract)

Abstract

It is necessary to get higher c-axis alignment of Nd2Fe14B grains in Nd-Fe-B magnets for higher-energy products. During the hot working process, where melt-spun flakes were hot pressed followed by die-upsetting, hot-pressed bodies showed roughly isotropic structure while c-axis alignments were developed during die-upsetting. In this report, we studied the relationship between the reductions during upsetting and the degree of the c-axis alignments and also tried to get the formula of this relationship. We prepared samples having different reductions and evaluated remanence, c-axis alignment and strains of each flake in the samples. c-axis alignments were evaluated using x-ray diffraction.1 Strains were measured using the sizes of each deformed melt-spun flake. In the range of 50%–70% reduction, remanence was lower in the surface layer than in the center. The difference in remanence in these two regions became smaller as the reduction became larger. The distribution of c-axis alignments and strains showed similar phenomena. Then we could propose the following formula showing the relationship between reduction and c-axis alignment: (σ − σ0)/(σi − σ0) = (1 − εz)4, where σ is standard deviation of c axis alignment and σ0, σi denotes the σ value at enough large strain and initial value of σ, respectively. εz means strain parallel to pressing axis.