Study On Crystal Microstructure And Magnetic Properties Of Fe₈₀Si₉B₁₁ Under Pretreatment

The unique microstructure of Fe-based amorphous alloy has resulted in its excellent magnetic properties and has always been favored by many scholars.However,due to the limitation of the preparation conditions,there are a large number of structural defects and residual stresses in the amorphous alloy.In this paper,the Fe₈₀Si₉B₁₁1 amorphous sample is taken as the research object.And the cryogenic and cryogenic+pulsed magnetic field pretreatment method is adopted.The effects of cryogenic treatment and pulsed magnetic field treatment and crystallization treatment parameters under cryogenic conditions on the crystallization microstructure and magnetic properties of Fe₈₀Si₉B₁₁1 amorphous materials were analyzed by XRD,DSC and VSM.The pretreatment of Fe₈₀Si₉B₁₁1 alloy showed that the XRD pattern of the pretreated sample had a broad diffuse peak at 2?=45°,and no sharp peak appeared at other positions,indicating that the sample was still amorphous.DSC test showed that the thermodynamic parameters of the pretreated samples changed.Under the condition of deep cooling+500 passes,the magnetic field treatment of 6T,7T and 8T on the alloy shows that the structural relaxation of the alloy is more obvious with the increase of magnetic field strength.The glass transition temperature T_g increases while the crystallization starting temperature T_x and the crystallization peak temperature T_p decrease.After crystallization,the precipitates of the pretreatment samples are all?-Fe,Fe₂B,FeSi,and the average grain size decreases with the increase of the magnetic field strength,which are 35.7 nm,31.4 nm,and 30.6 nm respectively.Under the condition of cryogenic+7T magnetic field strength,300,500,700 treatments of alloy show that the peak protrusion increases.After crystallization,?-Fe and Fe₂B were precipitated in 300 pretreatment samples,while?-Fe,Fe₂B and FeSi were precipitated in 500 and 700 pass pretreatment samples.The average grain size decreased with the increase of pulse number,which were 33.9 nm,31.4 nm,28.5 nm.DSC detection shows that the larger the number of pulses,the larger the crystallization volume fraction of the pretreated sample,and the T_g increases,and the T_x and T_p decrease.The annealing treatment of 763.15K,783.15K and 803.15K for the cryogenic+magnetic field pretreatment samples showed that the average grain size of the samples were 31.2 nm,28.5 nm,29.8 nm.The average grain size decreases first and the crystallization volume fraction increases with the increase of annealing temperature.However,the pretreated samples were treated with different annealing time for 20min,30 min,45 min.The results showed that the average grain size of the pretreated samples decreased at first and then increased with the prolongation of time.The crystallization volume fraction increased by 26.46%,28.92%and 30.61%,respectively.The VSM test results show that the Ms values of the amorphous/nanocrystalline samples after deep cooling+different magnetic field parameters are larger than the quenched samples.However,it is also found that as the number of pulses or the strength of the magnetic field increases,both Ms and Hc increase,and the latter increases more than the former,which shows that the infinite increase of magnetic field strength and pulse number is not necessarily beneficial to the magnetic properties of amorphous samples.At the same time,it is also found that the Ms value of the amorphous sample increases first and then decreases with the increase of annealing temperature or time after the deep cooling+magnetic field treatment,and Mr/Ms decreases first and then increases.Finally,Fe₈₀Si₉B₁₁1 amorphous samples were obtained under the condition of liquid nitrogen cryopreservation for 48h,magnetic field treatment?7T,700?and crystallization treatment?783.15K,30min?to obtain microstructures?-Fe,Fe₂B,FeSi.In this case,the saturation magnetization reaches the maximum value,and the remanence ratio is the smallest,and the soft magnetic property is considered to be excellent.