The Effects of Ribbon Thickness and Annealing Temperature on the AC Magnetic Properties of the Fe 81.5 B 14.5 Si 3 C 1 A
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THE EFFECTS OF RIBBON THICKNESS AND ANNEALING TEMPERATURE ON THE AC MAGNETIC PROPERTIES OF THE Fe 81.B 14.5Si3C1 ALLOY
S.C. IHIUANG,P.G. FRISCHMANN, F.E. LUBORSKY, J.D. LIVINGSTON, AND A. MOGRO-CAMPERO, General Electric Corporate Research and Development, Schenectady, New York, USA
ABSTRACT The a.c. magnetic properties measured at 60 Hz are found to be strongly affected by ribbon thickness and annealing temperature. These magnetic results are further characterized by observations on magnetic domain structure, crystallization, stress relaxation, and ribbon surface finish. INTRODUCTION The effect of some process variables on the properties of melt-spun amorphous metal ribbons has been reported recently (see Ref. 1 for a brief review). Of most interest is the finding that the soft magnetic properties are very sensitive to ribbon thickness as controlled by the casting speed [1-31. More specifically, it has been demonstrated that a ribbon should be cast at an optimum thickness in order to obtain the best d.c. magnetic properties [1,31. The degraded magnetic properties of thick ribbons were generally attributed to the reduced quench rate, but those of thin ribbons were not well understood. This work reports on the a.c. magnetic properties as influenced by the ribbon thickness as well as annealing temperature. The ribbon thickness was controlled by the melt delivery conditions (e.g., ejection pressure, nozzle slot size, and the crucible-wheel gap), while the casting wheel speed was kept constant [4). A number of ribbon characteristics relating to structure, stress, ribbon surface smoothness, and magnetic domain configuration were studied in order to obtain insights into the observed ribbon-thickness effect. EXPERIMENTAL Steady state casting of Fe81 B 4.Si3 C ribbons was carried out in air on a copper-1% chromium wheel with iAternaI water cooling. The casting wheel was rotated at a surface speed of 15 m/s and the wheel surface was maintained with wire brush at a "matte" finish during casting [5]. Variations in nozzle slot breadth (0.4 to 0.9 mm), ejection pressure (104 to 4 x 10 pascal), and crucible-wheel gap (0.35 to 0.7 mm) were made to change the ribbon thickness [4]. The resultant ribbon thickness was determined by calculation from ribbon weight divided by length, width, and density. The ribbon surface smoothness was studied by SEM and the ribbon cross section profile by metallography. The a.c. core loss and excitation were measured with sinusoidal flux at 60 Hz for straight ribbons (40 cm long) and toroids (20 turns on 7.5 cm diameter cores). The magnetic domain configuration was observed by the SEM technique [6]. Also, the stress relaxation was studied by annealing a ring [7], and the electrical resistivity by a four-probe d.c. technique [8]. Finally the magnitude and direction of the magnetic anisotropy were determined by a torque magnetometer using disk specimens etched out of the ribbon.
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212 RESULTS AND DISCUSSION The excitation of a straight ribbon (33 gm thick) near saturation induction is compared for
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