Study On The Thermal Transport And Magnetic Property In Metallic Glass

The physical and chemical properties of solid materials are primarily determined by their constituent elements and microstructure.Metallic glass,as a new type of alloy material,exhibits unique thermal transport and magnetic properties attributed to the combination of metal and atomic long-range disorder.Studying the thermal transport properties of metallic glasses is crucial for comprehending the formation ability of metallic glasses and developing new thermal barrier coating materials.Moreover,Fe-based and Co-based metallic glasses have exceptional soft magnetic properties and giant magneto-impedance effect.This dissertation predominantly focuses on studying the thermal transport properties of metallic glasses and the exploring of Co-based metallic glass wires with excellent magnetic properties.Additionally,the dissertation experimentally clarifies the cause of inverted hysteresis loops through the soft magnetic properties of Fe-based metallic glasses.The first part of this dissertation mainly focuses on researching the thermal transport properties of metallic glasses.Firstly,five types of bulk metallic glasses,namely La50Al35Ni15,Zr52.5Ti5Ni14.6Cu17.9Al10,Fe50Ni30P13C7,Hf47Cu29.25Ni9.75Al14 and Pd₄₀Ni₁₀Cu₃₀P₂₀ were selected for studying their thermal conductivity across different systems.The study found that the total thermal conductivity of these five materials increases with the temperature but remains below 10 Wm^-1K^-1 at 300 K,which is much lower than that of crystalline metallic materials.Moreover,in the range of 100-300 K,there was a linear dependence between their total thermal conductivity and temperature.In addition,the temperature coefficient of resistivity（TCR）of these five metallic glasses are about 10^-4 K^-1,indicating a weak temperature dependence of their resistivities.Using the Wiedemann-Franz law,we calculated the thermal conductivity of electrons and phonons respectively,and found that phonons are the primary carrier of heat conduction in metallic glasses at low temperatures,while electrons gradually replace phonons as temperatures increase becoming the main carriers of heat conduction in metallic glasses.Zr_52.5Ti₅Ni_14.6Cu_17.9Al₁₀ bulk metallic glass was then selected as a research object to investigate how structural changes affect its thermal conductivity behavior by vacuum annealing treatment at different temperatures to obtain relaxed structure state,partially-crystallized state and well-crystallized state.It is found that compared with as-castZr_52.5Ti₅Ni_14.6Cu_17.9Al₁₀ metallic glass,the alloy in the structural relaxation state is more conducive to the propagation of phonons in the material due to the reduction of free volume,thereby significantly improving phonon thermal conductivity.For other two crystallizedZr_52.5Ti₅Ni_14.6Cu_17.9Al₁₀ alloys,the appearance of NiZr₂ and CuZr₂ grains greatly caused a significant decrease in their resistivity compared to the as-castZr_52.5Ti₅Ni_14.6Cu_17.9Al₁₀ metallic glass,which in turn led to a significant increase in their electronic thermal conductivity.Additionally,compared with theZr_52.5Ti₅Ni_14.6Cu_17.9Al₁₀ metallic glass with a disordered structure,the appearance of grains also makes the atomic arrangement of the alloy denser resulting in further increase in the phonon thermal conductivity.The second part of this dissertation aims to clarify the cause of the inverted hysteresis loop.By systematically testing the hysteresis loops of Fe_73.5Cu₁Nb₃Si_13.5B₉metallic glass and its composite with the same composition of amorphous-nanocrystalline at room temperature,we observed the phenomenon that the hysteresis loops are inverted in both materials.Since metallic glasses are relatively homogeneous in structure,while amorphous-nanocrystals have obvious inhomogeneity in structure,and the magnetic anisotropy of both is very small,so the inverted hysteresis loop is not caused by structural inhomogeneity or magnetic anisotropy competition as reported in previous literature.In addition,we further analyzed the difference in the net coercivity of the three materials through the results of the hysteresis loop of metal Pd at room temperature,and determined that the remanence is the main reason for the reversal of the hysteresis loop.The third part of this dissertation preliminarily studies the magnetic properties of Co_68.15Fe_4.35Si_12.5-xCr_xB₁₅ metallic glass wires,including the effect of Cr doping on saturation magnetization and coercive force,as well as the effect of annealing treatment on effective permeability and giant magneto-impedance effect.It was found that an appropriate substitution of Si with Cr element,on the one hand,significantly improved the saturation magnetic induction of metallic glass wires.For example,the saturation magnetization of Co_68.15Fe_4.35Si_9.5Cr₃B₁₅ metallic glass wires at room temperature reached 0.9 T,which was higher than that of the Co_68.15Fe_4.35Si_12.5B₁₅ metallic glass wire are about 87%higher;on the other hand,Cr doping will also lead to Co_68.15Fe_4.35Si_12.5-xCr_xB₁₅（x=2,3）metallic glass wires have a more uniform atomic configuration over longer distances,resulting in the coercive force is significantly reduced.Selecting Co_68.15Fe_4.35Si_9.5Cr₃B₁₅ metal glass wire with relatively excellent soft magnetic properties for vacuum annealing and Joule annealing will further eliminate the residual stress during the preparation process,and significantly improve its magnetic permeability and giant magneto-impedance effect.In this dissertation,through the research on the thermal transport behavior of different systems of metallic glasses,the changes of the main heat-conducting carriers of metallic glasses in different temperature ranges are revealed,andZr_52.5Ti₅Ni_14.6Cu_17.9Al₁₀ metallic glasses are selected to change their microstructure through annealing treatment,and the link between thermal conductivity and microstructure are established.By systematically testing the hysteresis loops of Fe-based metallic glasses and amorphous-nanocrystals with the same composition,combined with the test results of metal Pd,the cause of the inverted hysteresis loops was clarified from the experimental point of view.In addition,this dissertation also preliminarily explores the magnetic properties of Co_68.15Fe_4.35Si_12.5-xCr_xB₁₅ metallic glass wire,and develops Co_68.15Fe_4.35Si_9.5Cr₃B₁₅ metallic glass wires with high saturation magnetization,high magnetic permeability and giant magneto-impedance effect,which is of great significance for the development of new magnetic sensors.