Backward extruded NdFeB HDDR ring magnets

Isotropic, submicron grained Nd15Fe77B8 powder has been prepared by applying the HDDR process. Fully dense isotropic magnets have been produced by hot pressing, textured compacts have been obtained by subsequent die upsetting. Radially oriented ring magnets have been prepared by backward extrusion of the hot pressed compacts. Very encouraging magnetic properties have been achieved, the remanence measured in the radial direction is B-r = 1.07 T with a coercivity of H-i(c) = 575 kA m. However, a decrease in alignment has been observed in the axial direction of the ring magnet. The effects of deformation temperature and speed hale been investigated. Magnetic properties and the physical and magnetic microstructure have been characterised by VSM. SEM and high-resolution Kerr-effect microscopy, the latter showing the formation of interaction domains, which indicate a high degree of texture in a fine grained material, in both the die upset and the backward extruded ring magnet produced from Nd15Fe77B8 HDDR material. (C) 1998 Elsevier Science B.V. All rights reserved.