| As a novel functional material, amorphous FeCo-based alloy which exhibits goodmechanical properties and excellent high-temperature soft magnetic characteristics has abroad application prospect in the field of high-temperature ferromagnetic material. Inthe miniaturization design of equipment and devices, FeCo-based alloy can expand theapplication temperature range, reduce the volume of the required magnetic material andreduce the space for heat dissipation. Metastable structure of amorphous alloycontributes to the complex phase transformation kinetics, which plays a vital role forunderstanding the structure of the alloy, the migration process of elements and thehigh-temperature structure evolution of amorphous alloys. The multi-componentincluding the combination of Fe and Co elements contribute to the excellent softmagnetic properties of alloys. To study the mechanism of the effective anisotropy, thefrequency spectrum of the magnetic permeability and the relationship between the softmagnetic characteristic and the composition can expand the application frequency band,improve the soft magnetic properties and provide theorectical and practical basis fordesigning and developing new ferromagnetic alloys.As the amorphous FeCo-based alloys were developed most lately, not much relatedresearch has been done yet; only few theories came from the research of Fe-based alloy.In the kinetics of phase transformation, Johnson-Mehl-Avrami (JMA) equation is basedon the assumption of two processes of crystal nucleation and growth in isothermalthermodynamics. Such theory based on theoretical assumptions is lack of universality,and can not explain the non-isothermal phase transformation process of amorphousFeCo-based alloy. In the area of soft magnetic properties, the precession model in themacroscopic magnetic domain theory is often used to explain the dynamicmagnetization process of alloys; however it is not for explaining the dynamicmagnetization process of the nano-scale ordered structure amorphous FeCo-based alloy.This dissertation carries out a series of research work about the kinetics of phasetransformation and soft magnetic properties of amorphous FeCo-based alloys. A seriescomponent of amorphous FeCo-based alloy was prepared with melt-spinning method, and thin films of amorphous FeCo based alloy were prepared with magnetron sputteringmethod. The thermal analysis data was deduced with differential thermal analysis andnano calorimetry method. The phase transition mechanism model of amorphous alloywas proposed, as well as the thermal analysis method based on heat capacity data. Thenon-uniform nanocrystals high frequency precession was simulated and validated withexperiment, providing new ideas to broaden the application of alloys.The main researchand innovations of this dissertation are as follows:1. Thermal analysis and data processing method for amorphous FeCo-based alloywas established, and the calculation method of activation energy based on Ozawaformula was developed. The relationship between phase transformation activationenergy and transformation rate was calculated from the experimental data of thermalanalysis, and the effect of doped elements on mechanism of activation energy wasdescribed. A new phase transition model has been established for the exothermicreaction of FeCo-based alloy ribbons for the first time, which has important physicalsignificance and engineering applications.This mode proposed an expression formulabased on the phase transition concentration, described the heat capacity characteristicasof alloys. By soling the fitting parameters of model, the mechanism of three thermalreactions in non-isothermal thermodynamics was revealed.2. The analytical and numerical analysis methods of distribution of magneticmoments in amorphous FeCo-based alloy grain were estabilished based onmicromagnetic theory, and consistent distribution and vortex distribution were found ingrains. The grain response characteristics of pulsed magnetic field were simulated, andmulti-resonance spectrum phenomenon of FeCo grain was found. The effectiveanisotropy constant of FeCo solid solution was calculated, the natural resonancecharacteristics of FeCo-based alloys was found. Non-uniform precession mode wasstimulated with the heat treatment process, which is consistent with experimentalobservations and could expand the resonance frequency band of alloys.3. The migration characteristics and mechanism of action of Al and Si elements inthe alloy was described with the elements doping research of amorphous FeCo-basedalloy ribbon. Griffith Crack gradient texture was found on rapid quenched alloy ribbons,and the texture can greatly improve the brittleness of the ribbons, which haveengineering significance on the powder process. In the non-isothermal process, Al element was found to be precipitated and oxided at the surface of the thin ribbon, whichcan significantly reduce the dielectric constant of the particle composite. A solidsolution formed by the Si element and FeCo lattice structure which has a low effectiveanisotropy was found.4. A device of array of the nano thermal conduction calorimetry was developedwith semiconductor technology. The device not only can be used for measuring thethermal performance of amorphous FeCo alloy thin films, but also can be widely usedfor thermal analysis of the magnetron sputtering film.The phase transition temperaturewas found to increase with increasing the content of the FeCo elements with theresearch of multi-component FeCo-based alloy thin films. The relationship between thethe films natural resonant frequency and heat treatment temperature was found, whichcould provide new design ideas for FeCo-based alloy thin filmsThe phase transition dynamics and soft magnetic properties of FeCo-based alloyribbon/film were researched in this disseratation; the effect of doping elements wasfurther studied. The phase transition mechanism and the spectrum excitationcharacteristics have developed the the theory of amorphous ferromagnetic material andperformance research system, which has important significance. |
