MICROSTRUCTURE OF HIGH-REMANENCE ND-FE-B ALLOYS WITH LOW-RARE-EARTH CONTENT

The microstructure and magnetic properties of bonded and fully dense m agnets produced from melt-spun ribbons of the composition RE4.5TM76GaB 18.5 have been investigated, where RE refers to a mixture of Nd and Dy , and TM refers to a mixture of Fe and Co. Results show that annealing overquenched ribbons with about 3 wt. % Dy and 3 wt. % Co at 700-degr ees-C can produce materials with H(ci) congruent-to 4 kOe, B(r) congru ent-to 11.5 kG, and (BH)max congruent-to 14.5 MGOe, the latter being c omparable to those of commercial ribbons containing three times as muc h Nd. The microstructure of annealed ribbons consists of about 30% Nd2 Fe14B grains, 65% Fe3B grains, and 5% alpha-Fe grains. The grains of a ll the phases are nearly spherical. The grain diameters are in the 30- 50 nm range. Hot-pressed magnets made from overquenched ribbons are fu lly isotropic, with magnetic and microstructural characteristics simil ar to those of the annealed ribbons. The high remanence and low coerci vity correlate well with the microstructure consisting of a uniform mi xture of the hard Nd2Fe14B phase and soft alpha-Fe and Fe3B phases.