Fabrication of bulk amorphous Fe67Co9.5Nd3Dy0.5B20 alloy by hot extrusion of ribbon and study of the magnetic properties

We report on the preparation of bulk amorphous Fe67Co9.5Nd3Dy0.5B20 by hot extrusion of melt-spun ribbons. X-ray diffraction studies were performed to check the structure of the as-spun ribbons and the consolidated bulk specimens. Differential scanning calorimetry (DSC) analysis of the amorphous ribbons revealed that crystallization proceeds in two stages. The first crystallization step leads to the formation of soft magnetic α-(FeCo) and (FeCo)3B and the second crystallization step corresponds to the formation of the hard magnetic (NdDy)2(FeCo)14B phase. The hysteresis loop of the as-spun ribbon reveals soft magnetic properties which change to hard magnetic behavior with enhanced remanence after annealing at 973 K for 7 min. X-ray diffraction analysis proves the presence of both soft and hard magnetic phases in the annealed sample. The viscosity of the powder obtained from crushed ribbons was investigated by parallel plate rheometry, showing a distinct viscosity drop in the supercooled liquid region that allows for easy consolidation of the crushed ribbons. The hot extruded sample that was subsequently annealed at 973 K for 7 min exhibits good hard magnetic properties with coercivity Hc = 218 kA/m, saturation magnetization Js = 1.36 T, maximum energy product (BH)max = 91.3 kJ/m3 and remanence Br = 1.18 T (after demagnetization field correction), respectively. C 2006 Springer Science + Business Media Inc.