HDDR PROCESS OF ND-FE-B WITH AN EXCESS OF INTERGRANULAR ND-RICH PHASEUNDER MAGNETIC-FIELD

High coercive isotropic Nd-Fe-B powders can be obtained using the nati on-disproportionation-desorption-recombination (HDDR) process. In orde r to produce anisotropic coercive powders, a static magnetic field of 7 T has been applied during the recombination stage, using an Nd-Fe-B alloy, with an excess of intergranular Nd/Cu eutectic. In parallel, th e behaviour of the Nd/Cu eutectic has been studied by in-situ neutron diffraction experiments: under hydrogen, the Nd/Cu eutectic is solid i n all temperature ranges, but under vacuum, hydrogen desorbs and the N d/Cu becomes liquid. To induce a rotation of the magnetic Nd2Fe14B cry stallites, it is necessary to reach a pronounced desorption of hydroge n. Hence, we have been able to produce anisotropic Nd-Fe-B material un der a magnetic field by increasing the holding time during the recombi nation stage of the HDDR process. (C) 1997 Elsevier Science S.A.