Effect Of High Magnetic Field On Crystallization Behavior Of Fe-B-C-Cu Amorphous Alloys

Nanocrystalline soft magnetic alloys produced from amorphous alloys have attracted great attention due to their excellent soft magnetic properties over the past two decades. Meanwhile, it has been demonstrated that high magnetic field (HMF) has remarkable influence on the diffusion process of element. Therefore, the aim of the work was to investigate the effect of high magnetic field on crystallization behavior of Fe-B-C-Cu amorphous alloys by isothermal annealing under HMF, differential scanning calorimeter (DSC), X-ray diffractometer (XRD), transmission electron microscopy (TEM) and the analysis methods of DSC.It has been found that the crystallization process of Fe-B-C-Cu amorphous alloys are promoted under high magnetic field by analyzing the change of the crystallization phase using XRD, TEM and DSC. The high magnetic field enhances the formation of a-Fe from the amorphous alloy at the appropriate temperature and annealing time. The enhancement of the HMF on the crystallization became stronger first and then became less obvious with the increasing annealing temperature and time. When the amorphous ribbons were isothermally annealed nearby the crystallization temperature (Tx) for 30 min or 30℃ below Tx for 60 min, the promoting effect of HMF on crystallization of Fe-B-C-Cu amorphous alloys was obviously observed.It turned out that the mechanisms are different, even though both of the crystallization processes of Fe84B10C6 and Fe83B10C6Cu1 amorphous alloys are promoted by HMF. By comparing the number of crystallites, crystallization volume fraction, average grain size and grain size distribution in the alloys annealed with and without magnetic field, we can see that the HMF only enhances the nucleation of crystallite α-Fe in the Fe84B10C6 amorphous alloy, and have no observable effect on the growth of α-Fe. However, the HMF greatly enhances the nucleation and growth of α-Fe in the amorphous alloy. The addition of Cu cause the formation of some dissociative Fe atoms in amorphous matrix due to the positive mixing enthalpy between Cu and Fe atom, and the diffusion of Fe could be enhanced by the applied magnetic field. It could be the possible reason why the HMF enhances the growth of α-Fe in the Fe83B10C6Cu1 alloy.The continuous DSC technique was used to investigate the crystallization kinetics of Fe83B1oC6Cu1 alloy annealed at 345℃ for 30min with and without a 12T magnetic field. It has been found that the temperature interval of crystallization wound be narrowed for the alloy annealed under high magnetic field, and the crystallization activation energy of the alloy annealed under high magnetic field was smaller than that of the alloy annealed without high magnetic field. What’s more, the activation energy in initial stage of crystallization obtained using the Doyle-Ozawa method was remarkably reduced by application of HMF.The soft magnetic property of Fe-B-C-Cu amorphous alloys was characterized using VSM. It has been shown that the soft magnetic properties of the amorphous alloys deteriorates in different degree after heat treatment whether or not a magnetic field is applied except for the sample annealed at the temperature 40℃ above Tx for 30 min which obtains about 90% volume fraction of the a-Fe phase. In longer annealing time or higher temperature, large grain size of the a-Fe phase makes an increase of coercivity. The soft magnetic property of the alloy could be enhanced by magnetic field under the condition of appropriate grain size and higher fraction crystallized.The effect of high magnetic field on crystallization behavior of Fe-B-C-Cu amorphous alloys was explained using the theory of nucleation of solidification. It turned out the crystallization process was promoted by HMF when the permeability of crystallite μ2 is higher than that of amorphous matrix μ1,i.e. (μ2-μ1)>0. Because the crystallite of Fe-B-C-Cu amorphous alloys is a-Fe, which belongs to be soft magnetic phase and possessing a permeability higher than amorphous matrix. So the theory of nucleation of solidification well counts for the effect of high magnetic field on crystallization behavior of Fe-B-C-Cu amorphous alloys.