Study On The Micro-physical Mechanism Of Magnetic Memory Induced By Changes In Stress And Structure

Ferromagnetic materials are the basic materials widely used in the field of machinery manufacturing,especially the main bearing structure of the equipment is made of ferromagnetic materials,and bears extremely complex working conditions during service.These components are prone to fatigue damage,leading to catastrophic accidents.How to perform quantitative damage detection on ferromagnetic components has always been an urgent problem in the engineering field.Metal magnetic memory testing technology has great potential in the early damage detection of ferromagnetic materials,but its micro-physical mechanism has not yet been clarified,which directly affects the quantitative application of magnetic memory technology.Therefore,this article explores its micro-physical mechanism from the phenomenon of magnetic memory induced by changes in stress and organizational structure.In this paper,45 steel is used as the research material,based on Lorentz transmission electron microscope,starting from static load.Study the effect of pretreatment process on the initial magnetic signal of the sample and the purification effect of heat treatment demagnetization on the initial magnetic signal of the sample;Discuss the change law of magnetic domain structure under the condition of compressive stress excitation;The influence of the inhomogeneity of the internal structure of the sample on the movement of the domain wall under the conditions of pressure excitation and external field excitation is analyzed.The main conclusions are as follows:(1)Under compressive stress excitation conditions,the change of the magnetic domain structure is affected by the magnitude of the stress and the position of the specimen.As the stress increases,the change of the magnetic domain structure shows a trend from mainly changing the area of the magnetic domain to changing the structure of the magnetic domain,and the closer to the force position,the more obvious the change of the magnetic domain structure.(2)Under the excitation of compressive stress,the magnetic domain produces irreversible magnetization reversal,and its structure is between the initial state and the stressed state,forming a memory effect on stress;Stress anisotropy affects the orientation of the easy magnetization axis of the sample.Under the excitation of compressive stress,the sample shrinks in the direction of pressure and stretches in the vertical direction.The vertical direction becomes the easy direction of magnetization,and the magnetization vector turns to this direction.(3)Microscopic defects such as grain boundaries and nano-scale holes have a pinning effect on the domain wall.The pinning strength increases with the size of the defect and decreases with the distance between the domain wall and the defect increases;The samples with non-uniform polycrystalline structure,the equivalent field generated by the stress is not enough to drive the domain wall to move.Under the excitation condition of an external magnetic field,the domain wall rapidly shifts and is pinned at the grain boundary to form two main domains with the position of the grain boundary as the boundary,enhancing the real magnetic signal of the component.