Abstract
Bulk exchange-spring magnets of Nd11Fe72Co8V1.5B7.5 and Nd9Fe76Co8V16B alloys were prepared by Spark Plasma Sintering (SPS) using the rapidly quenched ribbon powders. The effects of SPS process conditions on magnetic properties and structures were investigated. SPS is a type of solid compression sintering similar to hot-pressing (HP) and can be performed at lower temperature with a shorter holding time. Bulk magnets reached to approximately full density at a sintering temperature of higher than 650°C for 5 min. and had magnetically isotropic properties. They indicated the spring back phenomenon peculiar to exchange-spring magnets and consisted of multiphase of the Nd2Fe14B type phase and the α-Fe type phase. Grain growth did not occurred between the powders of the starting ribbons, but the fine crystals were observed inner the powders of the ribbons with an increase in the sintering temperature.
Optimum preparation conditions and magnetic properties were as follows: composition, Nd9Fe76Co8V1B6; surface velocity of the roller during melt spinning for starting ribbons, Vs=20 m/s; SPS condition, at 675°C for 5 min. under 490 MPa; magnetic and other properties, Br=0.99 T, Hcj=415 kA/m, (BH)max=107.8 kJ/m3, Hk/HcJ×100=23%, spring back ratio=40% and D=7.59 Mg/m3.
