The Research On Effect Of Magnetic Interaction On Structure Relaxation And Mechanical Properties Of FeNi-based Amorphous Alloys

Complex structural relaxation exists in amorphous alloys,which is closely related to their low temperature plasticity.Under the influence of magnetic field,magnetic atoms or clusters in amorphous alloys are rearranged,and the microstructure is changed,which leads to different structural relaxation and deformation behaviors.At present,the effect of magnetic interaction on relaxation and mechanical behaviors of amorphous alloys is still unclear.We selected FeNi-based amorphous alloys with tunable slowβ-relaxation activation energies（E_β）and Curie temperatures（T_C）as model materials,and systematically studied the effect of magnetic interaction on the structural relaxation,tensile properties and fracture behaviors of amorphous alloys.We prepared Fe_xNi_72-xSi_4.8B_19.2Nb₄（x=0,10,30,50,72）amorphous alloy ribbons by high vacuum arc melting and single copper roller melt-spinning method.Through the analysis of differential scanning calorimetry and nanoindentation,it was found that with the increase of Ni concentration,the glass transition temperature（T_g）,hardness and elastic moduli of amorphous alloys decrease.Through the analysis of thermogravimetry and vibrating sample magnetometry,it was found that with the increase of Ni concentration,T_C and saturated magnetization（M_s）of the amorphous alloys decrease.The results of dynamic mechanical analysis show that with the increase of Ni concentration,theα-relaxation peak of amorphous alloys moves to low temperatures,and E_βdecreases.With the replacement of Feby Ni the entropy of mixing of the system first increases and then decreases.This leads to the transformation of the dynamic mechanical relaxation spectrum of slowβ-relaxation from a shoulder to an excess wing,and then to a shoulder again.It was found that a relaxation peak appears at T_C（390 K）for Fe₃₀Ni₄₂Si_4.8B_19.2Nb₄amorphous alloy due to the structural change caused by the ferromagnetic transition.Larger preloading force and smaller strain suppress the relaxation peak.The loss moduli of Fe_xNi_72-xSi_4.8B_19.2Nb₄（x=30,50,72）amorphous alloys below T_g are reduced and the slowβ-relaxation is suppressed by applying a magnetic field of 45 m T during the dynamic mechanical test.The suppression effect of magnetic field on slowβ-relaxation weakens when the temperature is above T_C.Compared to the case under zero-magnetic-field annealing,Fe₃₀Ni₄₂Si_4.8B_19.2Nb₄amorphous alloy shows different relaxation behaviors and mechanical properties after magnetic annealing in different directions.After being annealed in a transverse magnetic field,E_βand E’’below T_g increase,and the slowβ-relaxation peak is enhanced.In contrast,applying a longitudinal magnetic field during the annealing process significantly reduces E_βand E’’below T_g,and suppresses the slowβ-relaxation peak.By analyzing the fracture morphology,it is found that plastic flows exist in the samples annealed by longitudinal magnetic field during tensile fracture.