The Study Of Magnetoelastic Behavior For Fe-Ga(Al) Based On Domain Rotation Theory

Fe-Ga(Al)alloys are new functional materials.Since the great magnetostriction performance of Fe-Ga(Al)alloys was found,they have been the hot area of research.The breakthrough in processing technology has led them to be more and more applied in actuator and sensor.Though extensive research has been done on Fe-Ga(Al)alloys,there is still neither a clear explanation about its magnetoelastic behavior,nor a comprehensive study on the factors that determine its magnetoelastic properties.These,however,are very important for the further exploration and utilization of Fe-Ga(Al)alloys.Based on the domain rotation theory,in this thesis(1)the effect of stress and magnetic field loading path on magnetoelastic coupling deformation for Fe-Ga and Fe-Ga-Al alloys was studied,and it was found that the magnetoelastic coupling deformation is loading path-dependent;(2)the anisotropy of ?E effect of Fe-Ga single crystal was systematically studied,and the effect of texture type and orientation density of polycrystal on ?E effect and magnetomechanical coupling factor was clarified;(3)the relationship between magnetic domain structure and magnetostriction,as well as that between the domain rotation process and magnetostriction,were explored.The effect of stress and magnetic field loading path on magnetoelastic coupling deformation in Fe-Ga and Fe-Ga-Al alloys has been revealed.Based on the Jiles-Thoelke model and Armstrong's assumption that magnetic moment distribution is energy-dependent,an energy-based anisotropic magnetic domain rotation model was developed.The magnetoelastic behaviors of Fe-Ga single crystal under different stress and magnetic field loading and unloading sequences were compared.The magnetoelastic deformation of Fe-Ga single crystal alloy is not only dependent on the loading sequence of stress and magnetic field,but also on the magnitude of both fields.The way the loading path affects the magnetoelastic coupling behavior is that when the loading paths are different,the free-energy-surface changes in different processes,which leads to different rotation ways for 90° magnetic domains.When the magnetic field and stress were not coaxial,the effect of angle 0 between magnetic field and stress on magnetoelastic deformation of Fe-Ga-Al single crystal was studied.The larger the? is,the smaller magnetoelastic deformation along[001]direction,as well as the smaller difference among the magnetoelastic deformation obtained by different loading sequences of magnetic field and stress.The effect of stress on the magnetostriction of Fe-Ga alloy has been clarified.With the compressive prestress,the saturation magnetostriction of Fe-Ga increases greatly.The prestress changes the distribution of free energy and the initial distribution of magnetic domains,which consequently enhances the saturation magnetostriction.On increasing the prestress,the static magnetic energy needed to make magnetic domains rotate quickly increases and the magnetic field also increases.The effect of grain distribution on the AE effect has been revealed.The strain-stress curves and Young's modulus-stress curves along different crystallographic directions were simulated by the domain rotation model.The dependence of ?E effect on the crystallographic directions was studied.The ?E effects of Fe-Ga single crystal along different crystallographic directions have great differences,and the ?E effect is anisotropic and symmetric.Based on the result from single crystal,the effect of grain distribution of polycrystal on AE effect was further studied.Seven types of texture which are often obtained in Fe-Ga alloys,each with three different texture intensities,were designed by MTEX,and their ?E effect and magnetomechanical coupling factor variation with stress and magnetic field were compared.The alloys having the same preferred orientation show a similar ?E effect and magnetomechanical coupling factor variation with the stress and magnetic field.The effect of texture intensity on the?E effect and magnetomechanical coupling factor depends on the preferred orientation of grain.The<100>oriented alloys,including<001>fiber textured,Goss textured and cube textured polycrystal,have a similar large ?E effect and magnetomechanical coupling factor.The texture intensity has a relatively small effect on the AE effect and magnetomechanical coupling factor for<100>oriented alloys.Compared to<100>oriented alloys,the<110>and<112>oriented alloys have much smaller ?E effect and magnetomechanical coupling factor.The ?E effect and coupling factor variation with stress and magnetic field in these two kinds of textured alloys are much more complex than that in<100>textured alloys.The domain rotation process during magnetostriction in Fe-Ga rolled sheet has been clarified.The magnetic domain pattern variation with magnetic field of rolled surface was observed by magneto-optic Kerr Microscopy in situ.According to the sample information and magnetostriction,different magnetic domain structures were constructed for different magnetization stage.In the demagnetized state,the magnetic domain structure of Fe-Ga rolled sheet was closure domain with lancet domain as supplementary domain,and when the magnetic field is larger than 8.3 kA/m the magnetic domains is lancet domains,which well explains the domain rotation process in the stage of slowly-increased magnetostriction.Using an equivalent stress,the magnetostriction of Fe-Ga polycrystal was simulated by an energy-based domain rotation model.The result fits well with the measured magnetostriction in rapid growth stage and saturation stage.These two models work as a complement to each other and clearly show the domain rotation process during magnetostriction.Work in this thesis enriches the study on magnetoelastic behavior of Fe-Ga(Al)alloys and clarifies its essence and mechanism from the views of domain rotation and energy change,which establishes the foundation for further exploitation and application of this alloy.