The Crystallization Kinetics And Magnetic Properties Of Fe_71.4Cu_0.6Nb₄Si₄B₂₀ Amorphous Alloy

In recent years,due to its excellent soft magnetic properties,amorphous alloys and nanocrystalline alloys have attracted more and more people.Since 1988,Yoshizawa et al developed FINEMET nanocrystalline alloy,Fe-Cu-Nb-Si-B amorphous alloys have been getting more and more attention.As we know,the nanocrystalline alloy has better soft magnetic properties under annealing in the vicinity of the crystallization temperature.And the result of the crystallization has great influence on the soft magnetic properties.But,the crystallization kinetics of Fe-Cu-Nb-Si-B amorphous alloys have rarely been studied.The Fe71.4Cu0.6Nb4Si4B20 amorphous alloy was prepared by melt-quenching method.The microstructure and properties of the alloy were investigated by metallographic microscopic analysis,scanning electron microscopy,X-ray diffraction(XRD),magnetic measurement and differential scanning calorimetric(DSC).And we study the crystallization kinetics of the amorphous alloy during the first crystallization stage and its microstructure with soft magnetic properties.The main conclusions are as follows:Under static conditions,the amorphous alloy has excellent soft magnetic properties,and the magnetic properties of amorphous alloys conform to the stress model.Under the dynamic condition,the complex permeability of the amorphous alloy decreases with the increase of the frequency,and the coercive increases with the intensity and frequency.Under the lower magnetic induction,the magnetic loss of the alloy is linear with the frequency,which is mainly due to the hysteresis loss under the 1 MHz.There are three crystallization stages in the crystallization of the amorphous alloy,and the characteristic temperature increases with the increase of the heating rate.The activation energies of the amorphous alloy calculated by Starink Ⅱ,Kissinger and Ozawa equation are similar.The local crystallization activation energy of the amorphous alloy was calculated by the FWO equation,the result shows that the activation energy increases with the increasing of the crystallization volume when the volume fraction is 20%～60%.During the process of isothermal crystallization,the isothermal temperature will lead to the decrease of crystallizing period and the shortening of crystallization time.In the 803 K～811 K,The average Avrami exponent is between 3 and 4.The amorphous alloy and the nucleation rate are gradually reduced with time until the nucleation rate is zero.The Arrhenius equation is used to calculate the activation energies of the local crystallization in the isothermal process Ec(x),the calculation error is large.The crystallization products of α-Fe+FeSi,Fe2B compound,NbB compound+ Cu in amorphous phase were obtained respectively.The amorphous alloy could obtain more excellent soft magnetic properties when quenched at 823 K,and then with the quenching temperature increases,soft magnetic properties have obviously declined;The quenched alloy should be nanocrystalline alloy.