Preparation of fully dense Nd-Fe-B magnets using semi-processed HDDR powders

Anisotropic fully dense Nd-Fe-B magnets can be produced by compacting the hydrogenation-decomposition-desorption-recombination (HDDR)-processed powder under an orienting magnetic field, and then hot pressing the green compacts. In this study, magnetic properties of the hot pressed magnets made from Nd12.7Dy0.3Fe64.3Co16.0B6.2Zr0.1Ga0.4 powders in the different stages of the HDDR process were investigated with regard to the degree of powder particle orientation. It was found that the powder in which small amounts of the decomposed NdH2 and alpha-(Fe, Co) phases remain (semi-processed powder), can be more highly oriented in applied magnetic fields less than 1190 kA/m as compared to the fully HDDR-processed powder. The magnet with B-r = 1.13T, H-cJ = 1280 kA/m, and (BH)(max) = 230 kJ/m(3) can be obtained by dehydrogenating the green compact of the semi-processed powder completely before hot pressing. (C) 2003 Elsevier Science B.V. All rights reserved.