Isotropic bulk exchange-spring magnets with 134 kJ/m3 prepared by spark plasma sintering method

Densification of exchange-spring magnet ribbons of NdxFe85-xCo8V1B6 (x = 7-11) alloys has been investigated. The starting ribbon powders containing amorphous parts were prepared by melt spinning and were compacted by using a Spark Plasma Sintering (SPS) method. SPS is a type of solid compression sintering similar to hot-pressing and the sintering promotion factor is self heat generation by electric discharges between particles when the on-off D.C. pulse is applied. The bulk magnets indicated the springback phenomenon, pointing to multiple phases of the Nd2Fe14B type and the alpha -Fe type, and had isotropic magnetic properties. With increasing Nd content, B-r decreased from 1.05 T to 0.82 T and H-cJ increased from 256 kA/m. to 832 kA/m. These changes were equivalent to those of the starting ribbons following annealing. The grain sizes of these bulk magnets were about 40 mn when x = 7-11. Under optimum preparation conditions, bulk Nd10Fe75Co8V1B6 magnet indicated (BH)(max) = 134 kj/m(3) (16.8 MGOe).