Formation And Properties Of Fe_82-xCr（Ni）_xB₈C₆Si₄ Amorphous Alloy

Fe based amorphous/nanocrystalline alloys are widely used in the fields of motors and transformers because of their excellent soft magnetic properties and corrosion resistance.Compared with traditional soft magnetic materials such as silicon steel,Fe based amorphous alloys have some advantages,but there are still many problems to be solved.For example,annealing is brittle and difficult to cut.At the same time,in order to ensure high B_s,it often maintains high Fe content,resulting in low amorphous forming ability and thermal stability.Moreover,it is often difficult to avoid the corrosion behavior of Fe based amorphous alloys due to manual contact in the production and processing process.Therefore,in this paper,Fe based amorphous ribbons were prepared by single roll strip casting method,and the effects of the addition of Cr and Ni on the formation ability,thermal stability,soft magnetic properties,mechanical properties and corrosion resistance of Fe based amorphous were studied by means of X-ray diffraction,differential scanning calorimetry,vibrating sample magnetometer,DC B-H instrument,scanning electron microscope,nano indentation and electrochemical workstation.In addition,the effect of heat treatment process on the microstructure and properties of the alloy was also studied in order to develop Fe based amorphous alloy with better comprehensive properties through the research of element addition and heat treatment process.The main results are as follows:（1）Study on the properties of Fe_82-xCr_xB₈C₆Si₄（x=0,2,4,6 at.%）amorphous alloy system.The addition of Cr improves the amorphous forming ability and thermal stability of the alloy.The width of supercooled liquid region increased from 27 K to42 K,and the initial crystallization activation energy increased from 133.8 k J/mol to246.3 k J/mol.The addition of anti ferromagnetic element Cr reduced the saturation magnetic induction of the alloy,but the coercivity H_cof the alloy decreased more significantly,from 15.22 A/m to 7.15 A/m.The results of nanomechanical tests show that the addition of Cr decreases the hardness and modulus of the alloy,and improves the room temperature plastic deformation ability of the alloy.When the content of Cr reaches 4 at.%,the maximum residual displacement d_nreaches 153 nm.After adding Cr element,the corrosion resistance of the alloy is significantly improved.The self-corrosion potential increased from-0.60 V to-0.03 V,and the self-corrosion current density increased from 26.77μA/cm²reduced to 2.07μA/cm².（2）Study on the properties of Fe₇₈Ni₄C₆B₈Si₄（x=0,2,4,6 at.%）amorphous alloy system.The addition of Ni improves the amorphous forming ability and thermal stability of the alloy.The width of supercooled liquid region increases from 27 K to35 K,and the initial crystallization activation energy increases from 133.8 k J/mol to200.4 k J/mol,which is inferior to that of Cr.The magnetic moment of Ni is smaller than that of Fe,and the B_sof the alloy decreases slightly from 1.63 T to 1.60 T,but the coercivity of the alloy is improved from 15.22 A/m to 10.54 A/m.The results of nanomechanical tests show that the addition of Ni decreases the hardness and modulus of the alloy,and improves the room temperature plastic deformation ability of the alloy.In particular,Fe₇₈Ni₄C₆B₈Si₄alloy can fold 180°without fracture,which is conducive to the cutting and processing of amorphous strips and the winding and forming of devices.The corrosion resistance of the alloy has been improved to a certain extent,and the effect is much lower than that of Cr element.The self-corrosion potential is only increased from-0.60 V to-0.50 V,and the self-corrosion current density is only reduced to 10.34μA/cm².（3）Fe₈₂C₆B₈Si₄,Fe₇₈Cr₄C₆B₈Si₄and Fe₇₈Ni₄C₆B₈Si₄amorphous alloys were annealed between 30℃below glass transition temperature（T_g）and crystallization temperature（T_x）.With the increase of annealing temperature,the B_sof the alloy also increases continuously,up to 1.79 T.The coercivity decreases first and then increases.The coercivity of Fe₇₈Cr₄C₆B₈Si₄amorphous alloy is as low as 3.49 A/m when annealed at 430℃.Reduction of free volume andα-The precipitation and growth of Fe（Si）phase make the hardness of the alloy increase continuously.When the annealing temperature is lower than T_g,the corrosion resistance increases with the increase of temperature.When the temperature is higher than T_g,the precipitation of nanocrystals increases the defect density in the alloy,and the corrosion resistance decreases,but it is better than the quenched alloy.（4）Fe₈₂C₆B₈Si₄,Fe₇₈Cr₄C₆B₈Si₄and Fe₇₈Ni₄C₆B₈Si₄amorphous alloys were treated at different times at T_g-30 K and T_g+20 K.At the temperature of T_g-30 K,the structure of the alloy relaxes,the internal stress of the alloy decreases gradually with the extension of holding time,and the soft magnetic properties and corrosion resistance are improved.When the annealing temperature is T_g+20 K,the alloy crystallizes,and the nanocrystalline phase precipitates in the amorphous matrix.With the increase of annealing time,the content and size of precipitated nanocrystalsα-Fe（Si）increase,and the B_sof the alloy increases,but the increase of magnetic anisotropy increases the coercivity.The growth of nanocrystals also worsens the corrosion resistance of the alloy.