High-remanence rapidly solidified Nd-Fe-B: Die-upset magnets (invited)

Abstract

The best starting materials for die-upset magnets are moderately overquenched melt-spun ribbons of Nd-Fe-B alloys with ∼20 at. % more rare earth than stoichiometric Nd2Fe14B. Remanence increases with increasing die-upset (DU) level, reaching a maximum of 13.5 kG at 70% DU for ternary Nd-Fe-B magnets, beyond which cracking limits performance. Remanence is also limited by nonuniform deformation, particularly for moderately die-upset magnets. Heat treatments, dysprosium substitutions, or low-level additives can be used to compensate for the decreases in coercivity which accompany increases in die-upset level. By die upsetting in stages and removing misaligned surfaces, a large Nd-Fe-Co-B-Ga magnet (∼30 g) has been produced with both a high remanence (14.2 kG) and a high-energy product (48.5 MG Oe).