Magnetic Properties on Bulk Exchange-spring Magnets in Nd-Fe-Co-V-B System Formed by Spark Plasma Sintering

摘要

Bulk exchange-spring magnets of Nd_(11)Fe_(72)Co_8V_(1.5)B_(7.5) andNd_9Fe_(76)Co_8V_1B_6 alloys were prepared by SparkPlasma Sintering (SPS) using the rapidly quenched ribbonpowders. The effects of SPS process conditions on magneticproperties and structures were investigated. SPS is a type ofsolid compression sintering similar to hot-pressing (HP) and canbe performed at lower temperature with a shorter holding time.Bulk magnets reached to approximately full density at asintering temperature of higher than 650 deg C for 5 min, andhad magnetically isotropic properties. They indicated the springback phenomenon peculiar to exchange-spring magnets andconsisted of multiphase of the Nd_2Fe_(14) B type phase andthe #alpha#-Fe type phase. Grain growth did not occurredbetween the powders of the starting ribbons, but the fine crystalswere observed inner the powders of the ribbons with an increasein the sintering temperature.Optimum preparation conditions and magnetic properties wereas follows: composition, Nd_9Fe_(76)Co_8V_1B_6; surfacevelocity of the roller during melt spinning for starting ribbons,V_s =20 m/s; SPS condition, at 675 deg C for 5 min. under 490MPa; magnetic and other properties, B_r = 0.99 T, H_(cJ) = 415kA/m, (BH)_(max) =107.8 kJ/m~3, H_k/H_(cJ) X 100 = 23percent, spring back ratio =40 percent and D = 7.59 Mg/m~3.