Proven technologies on high-performance Nd-Fe-B sintered magnets

Recently, we have newly developed the 460 kJ/m(3) magnet. B, value of this magnet shows 1.533 T that corresponds to almost 96% of the theoretical value of Nd2Fe14B compound. And the H-ej value of this magnet is kept at 784kA/m. One of the advanced technologies leading to this success is an improvement of the strip-casting alloy that has finer dendrites with scattered R-rich phase. Even though the rare-earth content of the alloy is only 12.3 at.% that is close to the stoichiometric 2-14-1 phase, the new alloy has finer dendrites with keeping an excellent orientation without the primary Fe phase. Furthermore, we have succeeded in stabilizing powder after milling with using some lubricants and to control the microstructure to be fine and uniform with keeping higher alignment of the 2-14-1 grains through sintering. Also, we have been investigating how to improve thermal stability and the corrosion resistance not only by treating surface coating but also by improving microstructure of magnets. As a result, we have been mass-producing high-performance magnets having 2.0 MA/m of H-cj for motor applications. In this paper, market trend of NdFeB sintered magnets is introduced and the latest processing technologies to produce higher energy Nd-Fe-B sintered magnets are described. (c) 2005 Elsevier B.V. All rights reserved.