Crystallization And Magnetic Properties Of Fe_68.35B_22.08Nd_5.57Nb₄ Bulk Amorphous Alloy

In the thesis, we study the crystallization and magnetic properties ofFe_68.35B_22.08Nd_5.57Nb₄ bulk amorphous alloys. Kissinger, Ozawa, Boswell, Staringkâ… andStarinkâ…¡methods are used to calculate the apparent activation energy Ea. Thecrystallization kinetics is studied by Matusita method., The precipitated phases of samplesafter holding 5 minutes at 750 centigrade are investigated by X-Ray Diffractions and theirshapes are observed by SEM. Using VSM to measure the hysteresis loops of differentdirections. The magnetic domain structures of samples after heat treatment are studiedusing the MFM technique.Ozawa method has the best precision in all five methods. The result using this methodis: E_a1=774kJ/m³, E_a2=413kJ/m³. The effective activation energy E_c1 is 1205 kJ/m³ and E_c2is 652kJ/m³. The precipitated phases of the first and second crystallization parameter are2.2 and 2.5, which indicating 2D nucleation and growth processes. Holding 5 minutes at750 centigrade, the precipitated phases of samples are composed by Nd_1.1Fe₄B₄,Fe₃B,α-Fe and unknown phases. Grains become refined after adding 12T magnetic field duringcrystallization. On the magnetic-field direction, the optimization magnetic properties are: H_c=57kA/m, M_r=214mT, (BH)_max=2952J/m³. During the magnetic-field heat treatment, the microstructure of precipitated phases have a tendency to arrange with some directionand the exchange coupled interaction between the grains have been enhanced. Thereforethe magnetic properties have improved.