Effect Of High Magnetic Field On Crystallization Behavior Of Fe-Based Amorphous Alloys

Fe-based amorphous alloys have attracted great attention due to their excellent magnetic,mechanical and corrosion resistance properties.Nanocrystalline soft magnetic alloys with outstanding soft magnetic performances can be prepared from amorphous alloys after suitable annealing.Meanwhile,it has been demonstrated that high magnetic field?HMF?has remarkable influence on the diffusion process of element and amorphous crystallization.Therefore,the aim of the studies was to investigate the effect of high magnetic field on crystallization kinetics and crystallization behavior of Fe-B-C-Cu and Fe-C-Si-B-P-Cu amorphous alloys by isothermal annealing under HMF,X-ray diffractometer?XRD?,differential scanning calorimeter?DSC?,transmission electron microscopy?TEM?,vibrating sample magnetometer?VSM?and the analysis methods of DSC.The main contents and conclusions of this study are as follows:Crystallization kinetics of as-spun Fe-B-C-Cu amorphous alloys and Fe₈₃B₁₀C₆Cu₁ alloy annealed under HMF have been performed by continuous DSC technique.It has been found that the Kissinger equation,Augis-Bennet equation,Ozawa equation,Lasocka equation and VFT equation could well describe the relationship between the characteristic temperature and the heating rate of the Fe-B-C-Cu metallic glass.The apparent activation energies calculated by the Kissinger equation are less than others.Meanwhile,the apparent activation energy value of Fe₈₃B₁₀C₆Cu₁ amorphous alloy is higher than than of the Fe₈₄B₁₀C₆ amorphous alloy.The relationship between the crystallized volume fraction and apparent crystallization activation energy for the Fe-B-C-Cu amorphous alloys has been obtained using Doyle-Ozawa method.It has also been proved that the addition of the Cu elements increases the apparent crystallization activation of Fe-B-C-Cu amorphous alloys.The curve reflecting the mechanism of crystallization of Fe-B-C-Cu amorphous alloys have been fitted using JMA and NGG equations,and it has been found that the annealing udner high magnetic field did not change the mechanism of crystallization of Fe₈₃B₁₀C₆Cu₁ amorphous alloy.The effect of high magnetic field on crystallization of Fe₇₆C₇Si_3.3B₅P_8.7 amorphous alloy has been stuied.The Kissinger equation and VFT equation could well describe the relationship between the characteristic temperature and the heating rate of Fe₇₆C₇Si_3.3B₅P_8.7 amorphous alloy.The Doyle-Ozawa method was used to obtain the relationship between the crystallized volume fraction and apparent crystallization activation energy of the alloy.Meanwhile,the mechanism of crystallization of Fe₇₆C₇Si_3.3B₅P_8.7 amorphous alloy has been analyzed using JMA and NGG equation.The high magnetic field could enhance the formation of ?-Fe nanocrystalline from Fe₇₆C₇Si_3.3B₅P_8.7 amorphous alloys and made the distribution of the a-Fe more uniform.The influence of high magnetic field on the crystallizaiton behavior of the Fe_75.3C₇Si_3.3B₅P_8.7Cu_0.7 amorphous alloy has been invesitaged.It has been found that the Kissinger equation,Augis-Bennet equation,Lasocka equation,Ozawa equation and VFT equation could well describe the relationship between the characteristic temperature and the heating rate of the Fe_75.3C₇Si_3.3B₅P_8.7Cu_0.7 amorphous alloy at the heating rate used in the thesis.The apparent crystallization activation energy and crystallzation mechanisms of the Fe_75.3C₇Si_3.3B₅P_8.7Cu_0.7 amorphous alloy are different with those of the Fe₇₆C₇Si_3.3B₅P_8.7 amorphous alloy.The high magnetic field could enhance the the nucleation rate of a-Fe,and refine the grain size of a-Fe in the alloys.The soft magnetic property of Fe_75.3C₇Si_3.3B₅P_8.7Cu_0.7 alloys was characterized.It has been found that the the magnetization of the alloys increases with the annealing temperature and time,and the coercivity of the alloys has no obvious change.The influence of the HMF on the the nucleation rate and the grain size of the a-Fe greatly improves the magnetic properties of the Fe_75.3C₇Si_3.3B₅P_8.7Cu_0.7 alloys.The glass forming ability of Fe_76-xC₇Si_3.3B₅P_8.7Cu_x?x=0,0.7?amorphous alloy has been decreased by adding Cu.Furthermore,the activation energy of crystallization decreases with increasing Cu content.Because of the large positive heat of mixing enthalpy between Fe and Cu,the Cu enriched clusters can be readily formed which will supply nucleus to promote the formation of ?-Fe,and thereby improve the magnetic properties of the alloys.