Study On Crystallization Behavior And Properties Of FeSiB Amorphous Alloys Under Strong Magnetic Field

The high performance and size miniaturization of power electrical applications require the use of a soft magnetic material having a high saturation magnetic induction(Bs)as a magnetic core.Fe-based amorphous materials,which are widely studied and applied at present,have high Bs and excellent soft magnetic properties,but have poor performance in high frequency.However,after the amorphous crystallizing,the formed amorphous/nanocrystalline soft magnetic composite material can have a high Bs of Fe-based amorphous,can also be used under high frequency conditions,and the high temperature stability is also greatly improved.It has become an important direction in the development of soft magnetic materials.At this stage,strong magnetic field is an effctive tool to control the crystallization process of amorphous alloys.In this thesis,the effect of magnetic field on the crystallization behavior and properties of FeSiB amorphous alloys is studied by annealing and heat treatment of FeSiB amorphous alloys.The FeSiBNbCu amorphous alloy was subjected to high magnetic field annealing heat treatment,and it was investigated whether the high magnetic field heat treatment could further improve the crystalline structure and properties of the alloy under the conditions of adding Cu and Nb elements.In this thesis,the amorphous forming ability of FeSiB alloy is analyzed by X-ray diffraction;the thermal stability of FeSiB amorphous alloy is analyzed by DSC;the magnetic properties of the alloy are analyzed by VSM;The belt is annealed and heat-treated;the microstructure of FeSiB and FeSiBNbCu amorphous alloys after heat treatment is oBserved by TEM,and the crystallization behavior and properties of FeSiB amorphous alloys are studied.Draw the following conclusions:(1)Through studying the microstructure of Fe81Si4B15 and Fe83Si4Bi3 amorphous alloys under annealing and heat treatment at different temperatures and different magnetic field strengths for 30 min,it was found that the nucleation of the a-Fe phase with the increase of the applied magnetic field strength during heat treatment,the number of points is increased,the grain size is reduced,the crystallization rate is improved,and the grain size distribution is more uniform.(2)The magnetic properties of the Fe81Si4B15 and Fe83Si4B13 amorphous alloys were measured by annealing and heat treatment at different temperatures and different magnetic field strengths for 30 min.It was found that the value of Bs increased with the increase of the crystallinity of the ?-Fe phase,and the value of Hc decreased with the decrease of the a-Fe grain size.The Bs value of Fe81Si4B15 alloy increased from 1.53 T to 1.78 T,and the Bs value of Fe83Si4B13alloy increased from 1.56 T to 1.88 T.(3)Kinetic and thermodynamic study on crystallization of Fe81Si4B15 and Fe83Si4B13 amorphous alloys,it is found that the application of a magnetic field can effectively reduce the nucleation energy barrier and reduce the critical nucleation size of the ?-Fe phase.It can increase the nucleation rate of ?-Fe phase and increase the number of nucleating particles.In addition,with the increase of the applied magnetic field during the heat treatment,the B content in the a-Fe phase decreases,and B overflows from the ?-Fe phase into the amorphous matrix,which increases the stability of the amorphous matrix and suppresses the diffusion of Fe atoms in the amorphous matrix,and the effect of inhibiting the growth of the ?-Fe phase is achieved.Therefore,the external magnetic field during heat treatment can increase the number of ?-Fe phase nucleation particles and refine the ?-Fe phase grain size.(4)By studying the microstructure of Fe76Si13B8Nb2Cu1 amorphous alloy ribbons heat-treated at 773 K with an applied magnetic field strength of 0 T and 12 T,it was found that Fe76Si13B8Nb2Cu1 amorphous alloy can also refine the ?-Fe phase grains by strong magnetic field heat treatment,it can refine the grain size of ?-Fe phase,increase its nucleation particle number and crystallization rate.The grain size of the ?-Fe phase was reduced from 20 nm to 12 nm.The increase in the crystallization rate of the precipitated phase ?-Fe increased the value of Bs from 1.21 T to 1.49 T under this condition.