Relationship Between Melt Characteristics And Rribbon Properties Of FeSiB(P)-based Amorphous Soft Magnetic Alloys

Owing to the combination of excellent soft magnetic,mechanical,and electrochemical properties,amorphous soft magneitic alloys are widely used in the structural,functional and environmental protection fields.With the rising importance of saving energy and reducing greenhouse gas emissions,the advantages of Fe-based amorphous soft magnetic alloys should provide an option for smaller,lighter,and more efficient power electronic components,which in turn demands the development of new Fe-based soft magnetic amorphous alloys exhibiting both larger higher glass-forming ability and higher saturation magnetization.In this thesis,a deep understanding on the influence of melt characteristic and parameter variation on the surface quality of ribbons were brought up and discussed based on cluster theory.A series of novel FeSiBP amorphous soft magnetic alloys combined with high glass forming ability and excellent soft magnetic properties were developed by systematic alloy compenent design and parameter optimization.The influence of P content on the glass-forming ability and Fe content on the higher saturation magnetization of FeSiBP soft magnetic amorphous alloys based bulk metallic glasses were examined and corresponding mechanism was explained.The main results are drawn as follows:Ab initio molecular dynamics simulation shows obvious splitting of the second peak in both the total and partial structural function?gMM '?r?,M,M ' =Si,B?of two typical Fe-based alloy melts(Fe₇₈Si₉B₁₃ and Fe₇₆Si₉B₁₀P₅)during the rapid solidification,which suggests formation of the amorphous alloys.The average coordination number of Fe atom increases from 12 to 13 in the process of rapid solidification.Content of the dominant cluster with B atom in the center also increases rapidly and,meanwhile,the diffusion coefficient decreases.There is small possibility for Si and B atoms to have the first nearest neighbor relation with themselves or each other,although the second nearest neighbor arrangements dominate correlation of Si and B atoms.P atom has not the first nearest neighbor relation with itself or with Si and B atoms and thus there is strong evading effect for P atoms together with the Si and B atoms.The simulations also confirmed free energy of the icosahedron cluster lower than cluster with body-centered cubic configuration.The geometrical configuration of the clusters depends on the atomic packing density that closely related to the rotational symmetry.Influence of temperature and heat retaining time on the viscosity of FeSiB?P?amorphous alloys was studied systematically by measurement of vicosity of the alloy melts during heating cycle using viscosimeter.In the heating process,the viscosity of the alloy melts drops suddently at temperature ranging from 1350? to 1400? and a possible reason can be ascribed to appearance of the clusters that are not favorable for the melt flowing at this temperature range.The viscosity hysteresis was also found during the heating cycles.Influence of the heating cycle on the property of the amorphous ribbons has been studied by comparison of the strips prepared below and above the temperature responsible for the rapid drop of the melt.If the melt was heated above this temperature,the consistency of good surface quality was promoted because of decrease of bubbles of the wheel-side and roughness of the air-side of the ribbon.Based on the experimental results,the casting temperature,the ejection pressure,the distance between the nozzle and copper roller and the rotation speed of the copper roller for preparation of the amorphous ribbon with high quality have been determined to be 1300 ?,30kPa,0.3 mm and 20 m/s respectively.The thickness of the ribbon increases as increasing both the distance between the nozzle and copper roller and casting temperature and decreases as accelerating the speed of roller.However,the decreasing tendency of the thickness becomes gentle when the speed exceeds 30 m/s.By adjusting P content heat treatment parameters,Fe₇₈Si₉B₁₀P₃ bulk metallic glass with critical size of 1.5mm was prepared.Novel Fe₈₂Si₄B₁₁P₃ soft magnetic amorphous alloys with high saturation magnetic flux density of 1.66 T and low coercivity 2.2 A/m were first prepared by further optimization of the Fe content and heat treatment conditions.