Effect Of Magnetic Field Annealing On Soft Magnetic Properties Of Amorphous And Nanocrystalline Alloys

In this thesis, we investigated the effect of different annealing temperature and method of magnetic field annealing on the static magnetic properties of Fe₆₅Co₁₅Si₅B₁₅, Fe₅Co₇₀Si₁₅B₁₀ andFe₅Co₅₈Ni₁₀Si₁₁B₁₆ amorphous alloys. In addition, the sensitivities of transverse magnetic field annealing were also compared between above amorphous alloys and nanocysralline alloys. At last, to deeper understanding the change of magnetism,the magnetostriction and high-temperature permeability in magnetic annealing Fe₆₅Co₁₅Si₅B₁₅ amorphous alloys were explored.The influences of longitudinal and transverse magnetic field annealing upon the hysteresis loop and static magnetic parameters of Fe-, Co-, CoNi-based amorphous alloy were compared and analyzed in this paper. Vacuum pre-annealing was performed in order to eliminate the internal stress. The results showed that the samples'hysteresis loop shape can be modulated by the magnetic anisotropy energy induced in process of pre-annealing: longitudinal magnetic field annealing squares the loop shape, and the max permeability (μ_m) and remanence ratio ( B_r / B_s) increase with the annealing temperature rising; on the contrary, transverse magnetic field annealing narrows the loop shape, and the permeability tends to be constant. After vacuum annealing, the magnetic properties deteriorate. The magnetic properties of Fe–based amorphous alloy become more worse after pre-annealing and magnetic field annealing, but the magnetic properties of CoNi-based amorphous alloy are improved.The saturation magnetostriction(λ_s) of Fe-based amorphous alloy in longitudinal magnetic annealing was measured, the result showed that there is not consistent with changes ofλ_s and coercive force H cin the sample of magnetic annealing, namely, with the ascending of temperature,λ_s is increasing , but coercive force H cwill be appear to the peak value. So we draw a conclusion that the saturation magnetostrictions is not leading role. According to the discussion of KelenMüller to the effect factor of coercive force, the appearing peak value of coercive force is possibly due to the exchange energy of short-range order and the increasing of proclivity fluctuation of local anisotropism.By measuring the change of initial permeability with temperature after magnetic annealing of amorphous alloys. we found that the initial permeability will drop to a lower value after a higher temperature magnetic annealing, and maintain constant before Curie temperature of amorphous phase, this result is similar to the change of nanocrystalline (Fe_0.25Co_0.7573.5Si₍13.5_B9Nb₃Cu₁ alloy in higher annealing temperature. In this paper, we also explored the crystallization of Fe₆₅Co₁₅Si₅B₁₅ under a special annealing condition and obtained the nanometer grain size. This result is valuable for developing the new high-temperature soft magnetic materials.In addition, amorphous and nanocrystalline to magnetic sensitivity in the transverse magnetic field annealing were compared in this paper. The result showed: Fe-based amorphous alloys is more sensitive to magnetic annealing than that of Co-based amorphous alloys and nanocrystalline alloys.