Mechanical Properties And Stress Torsion Magnetoimpedance Effect Of Co-Based Metallic Microfibers

Based on the Giant Magnetoimpedance Effect?GMI?,the magnetic sensors have outstanding advantages such as high sensitivity,fast response,low power consumption,small size,etc.,and have become one of the typical representatives of the third generation magnetic sensors.This paper systematically analyzes the effect of current modulation on the microstructure,mechanical and magnetic properties of rotated dipping Co-based metallic microfibers,and comprehensively evaluates the mechanical properties of which from the aspects of tensile mechanical properties,fracture reliability analysis,cyclic loading and flexibility characteristics.Furthermore,combined with the fracture morphology,the"structure-mechanical property-fracture mechanism"relationship model was established to realize the adjustment and optimization of the GMI effect,and revealed the influence laws of the magnetoelastic anisotropy,spiral anisotropy,and the coupling effect on the GMI effect,to provide a theoretical basis for the development and engineering application of stress torsion magnetic sensors.The research results show that the Co-based metallic microfibers with typical amorphous structure exhibit a favorable amorphous forming ability and thermal stability.The prepared microfibers have good tensile mechanical properties,and the average tensile strength R???_m of which is about 3.7 GPa.Appropriate intensity current annealing can improve the mechanical properties of the microfibers,which is related to the effectively inhibition of the rapid growth of cracks by nanoclusters uniformly distributed in amorphous matrix.And among which,the microfibers annealed by 90 m A have a better fracture reliability with the breaking threshold ?_? of 2.7 GPa.Under the tensile stress,the fracture of the microfiber is an oblique fracture with the fracture angle of about 50°,and there are a large number of vein-like patterns and a small amount of droplets on the fracture surface.During torsion,the spiral vein patterns appear on the fractures,and while under the stress-torsion,the"stress torsion steps"appear.In short,the fracture process of Co-based metallic microfibers is a typical micropore aggregation fracture,and the nanopores are the origin of crack initiation and extension.The results of cyclic loading show that with the increase of the number of cycles,the stress-strain curves of the metallic microfibers appear nonlinear hysteresis,and its tensile strength R_m is 3.1 GPa which is slightly lower than R???_m.iimultaneously,the Co-based metallic microfibers exhibit a good flexibility,and a large number of shear bands appear at the kink bends of the metallic microfibers.The Co-based metallic microfibers exhibit excellent soft magnetic properties before and after current modulation.With the rising of annealing current intensity,the index value of GMI performance increases firstly and then decreases,among,the GMI effect of the microfibers annealed at 65 mA is better,and at f=5 MHz,the maximum impedance change ratio[?Z/Z_max]_max and the maximum magnetic field response sensitivity ?_max are 273.99%and 94.00%/Oe,respectively.The Joule heat generated by the proper intensity annealing current can eliminate the internal residual stress,at same time genrated a toroidal mgnetic field to regulate the distribution of the annular magnetic domain,improve the circular magnetic permeability,and thus improve the GMI effect.The stress-torsion magnetic impedance effect is closely related to the magnetoelastic anisotropy and helical anisotropy.When tensile stress acts,the magnetoelastic anisotropy can increase the circumferential domain wall energy of the metallic microfibers and promote the circular permeability,further to improve the GMI effect.When f=3 MHz,the[?Z/Z_max]_max reaches at 293.63%under the maximum tensile stress of 482 MPa.When torsion and stress-torsion acts,the helical anisotropy will decrease the toroidal domain wall energy,induce axial anisotropy,and reduce the toroidal permeability.