In-Situ Study On The Mechanism Of Stress-induced Magnetic Anisotropy In Fe-based Alloy Ribbons

Fe-based amorphous alloys have excellent soft magnetic properties and are widely used.However,due to its stress sensitivity,the efficiency of amorphous soft magnetic devices can not be well improved.About 20% of the theoretical predicted values are restrained by stress,and the mechanism of stress-induced magnetic anisotropy in Fe-based amorphous ribbons is still unclear,so it is difficult to guide production to solve the related technical problems.Therefore,it is significant to study the mechanism of magnetic anisotropy induced by stress annealing and to establish a theoretical model that everyone agrees with.In this paper,the macro-elongation of the sample was observed and recorded,the giant magneto-impedance ratio curve and the magnetic anisotropy of the sample were measured.The microstructure of annealed and tempered samples was observed in situ by the Shanghai Synchrotron Radiation Facility,and the microstructure data of the samples,such as lattice anisotropy,micro-strain and grain size,were obtained.By comparing the experimental data of the stress annealing and tempering samples,some conclusions consistent with the experimental results were obtained,and a model which can explain the mechanism of magnetic anisotropy induced by stress annealing was established.The conclusions are as follows:1.Magnetic anisotropy of Fe-based alloy ribbons after stress annealing and tempering:There is a good linear relationship between the magnetic anisotropy induced and the annealing stress in stress annealed samples;There is also a good linear relationship between the strain and the annealing stress in stress annealed samples.The lattice anisotropy,macroscopic strain and magnetic anisotropy induced by stress annealing can not be completely eliminated by multiple tempering.Although the lattice anisotropy caused by residual stress of stress annealing is the main cause of magnetic anisotropy,it is not the only reason.In the process of stress annealing,nanocrystalline grains are congregated by the creep plastic deformation of amorphous substrate,and it is also an important cause of magnetic anisotropy induced by stress annealing.Moreover,the magnetic anisotropy induced by the directional aggregation of nanocrystalline grainsthe caused by the creep plastic deformation of amorphous substrate during stress annealing can not be completely eliminated by tempering method.The samples annealed at different temperatures under the same stress have different soft magnetic properties.The macroscopic strain and maximum impedance ratio of samples annealed below 500? increase linearly with the increase of annealing temperature.However,the magnetic anisotropy and the optimum driving frequency decrease linearly with the increase of annealing temperature.2.Microstructure of stress annealed Fe-based alloy ribbons:In the samples annealed at different temperatures,the crystallization peaks begin to appear at 500 ?,the higher the temperature is,the more obvious the crystallization peaks become,and the crystal peaks appear completely at 530 ?.All the samples annealed at 540 ? have obvious crystallization peaks,and there is no obvious relationship between the annealing stress and the annealing stress.With the increase of annealing stress,the lattice anisotropy of the sample increases gradually.The lattice anisotropy of the sample annealed with constant stress decreases slightly with the increase of annealing time,and its change rate is much smaller than that of the sample with increasing annealing stress.The lattice anisotropy of annealed samples has a linear relationship with the annealing stress.In stress annealed samples,the larger the annealing stress,the smaller the grain size of the nanocrystalline.3.In-situ observation results of macro-strain and microstructure change in Fe-based amorphous ribbons:When the sample is annealed at 380 ?,the creep of the amorphous phase leads to a sharp increase of the elongation,and the macro-strain of the sample increases sharply.During the tempering process,the macro-strain of the sample decreases gradually.The first tempering decreases a lot,but the second and the third tempering decreases little,and the two variation curves are almost coincident.In the free annealing process,the micro-strain curves parallel to the stress direction and perpendicular to the stress direction almost coincide with each other.In the process of stress annealing,the micro-strain parallel to the stress direction is stretched andcompressed in the perpendicular to the stress direction.During the tempering process,the micro-strain parallel to the stress direction decreases gradually,and the micro-strain compression amount perpendicular to the stress direction decreases.Their change behaviors are similar to the holding stage of the free annealing process.In the process of loading stress,the micro-strain of the sample parallel and perpendicular to the direction of stress(tensile and compressed)increases with the increase of stress,and there are linear relationships.