Recent developments in the sintering of NdFeB

Sintering plays a major role in the production of fully dense rare-earth permanent magnets. The sintering of these magnets is assisted by a ran-earth rich, grain boundary phase, which is liquid well below the sintering temperature and wets the surface of the hard magnetic (Nd2Fe14B) matrix grains. As well as aiding densification, this phase plays an important role in smoothing and isolating grains to produce a microstructure conducive to good magnetic properties. In this paper, previous studies of sintering in NdFeB-type magnets are reviewed briefly and recent investigations in these laboratories are described. In these studies, dilatometry has been used to study densification in NdFeB powder compacts over a range of temperatures and times. The effect of composition on the rate of densification was also investigated using a powder blending technique to vary the composition prior to sintering. Rare-earth hydrides were employed to vary the proportion and composition of the Liquid phase during sintering. (C) 2001 Elsevier Science B.V. All rights reserved.