| Iron-based amorphous/nanocrystalline alloys possess unique soft magnetic, mechanicalproperties and relatively low material cost, which is considered to be have potentialengineering applications as functional and structural materials. However, this alloy has somedisadvantages including low glass forming ability, low temperature difference between thefirst and second crystallization temperature, low Curie temperature of amorphous phase andvery poor ductility at room temperature. These disadvantages severely limit their wideengineering application. Moreover, the mechanism of the permeability, coercivity and brittlefracture is not well understood. For industrial applications and academic research, it is ofgreat interest to develop new iron-based bulk amorphous/nanocrystalline alloy with good softmagnetic property in addition to excellent mechanical property. This issue has been actuallythe subject of intense research in recent years.The chemical composition of amorphous alloy was designed by "Miedema Model","element substitution","binary eutectic rules" and "elastic module criterion". The amorphousmelt-spun ribbons with superior soft magnetic property and glassy powders with pure metalelements were prepared by melt-spinning and mechanical alloying method, respectively. Thehigh density of bulk iron-based amorphous and its nanocrystalline composite was formed byspark plasma sintering technique. Effects of milling time, sintering temperature and annealingtemperature on the evolution of microstructure and related properties were systematicallyinvestigated. Meanwhile, crystallization kinetics, densification behaviors, and the mechanismof the permeability, coercivity and brittle fracture of the amorphous alloys were alsoinvestigated.Formation enthalpy for iron with common transition metal and metalloid elements to formbinary intermetallic compounds was calculated on the basis of semi-empirical thermodynamic"Miedema theory". The compositions were selected through "element substitution","binaryeutectic rules" and "elastic module criterion". We successfully developed a series ofFe81Cu2Nb3Si14, Fe69Co8Nb7-xVxB15Cu1(x=0,2,5,7at.%) amorphous ribbons, Fe-Nb-X(X=Al, Zr, Ti, Ta) glassy powders and Fe94-xZr2Nb4Bx(x=10,15,20) supersaturated solidsolution nanostructured powders.The Fe81Cu2Nb3Si14amorphous ribbons with excellent soft magnetic properties, such assaturation magnetization up to142.15emu/g, coercivity as low as0.32Oe, curie temperature310.11℃. Fe81Cu2Nb3Si14amorphous powders were prepared by ball milling of melt-spun ribbons, then bulk Fe81Cu2Nb3Si14compacts were consolidated by spark plasma sintering.The crystallization of Fe81Cu2Nb3Si14amorphous powders proceeds through two reactionsduring SPS. Namely, amorphous→amorphous+α-Fe(Si)→α-Fe(Si)+Cu+Nb5Si3.Sintering temperature has significant effects on the densification, microhardness and magneticproperties of the compacts. With an increase in the sintering temperature, the relative density,microhardness and saturation magnetization of the sintered samples improved obviously, butthe coercive force decreased at the beginning and then increased with the increase of sinteringtemperature.On the basis of Fe81Cu2Nb3Si14composition, a new multi-element Fe69Co8Nb7-xVxB15Cu1(x=0,2,5,7at.%) amorphous alloys were developed through a method of "elementsubstitution". It is found that increasing V content can reduce glass forming ability, thermalstability and coercivity, but increase saturation magnetic flux density and Curie temperature ofamorphous phase. The desirable soft magnetic property in these amorphous alloys is x=7, andV content of x=2amorphous alloy has the widest heat treatment temperature range. Thesystem of amorphous alloys was taken on heat treatment in vacuum quartz tube. When Ta<Tg,The decrease of Hcfor annealed amorphous ribbons as result of relaxation of the internalstress of the as-quenched amorphous alloy. As Tx1<Ta<Tx2, the saturation magnetic fluxdensity increased due to the partial crystallization of amorphous precursors to create ahomogeneous distribution of bcc α-Fe nanocrystals within a residual amorphous matrix. Themagnetic properties drop rapidly when Ta>Tx2. This may be caused by grain growth andparamagnetic phase formation which hinder the magnetic coupling between the ferromagnetica-Fe grains. Fe69Co8Nb5V2B15Cu1amorphous after annealed at580℃for1h has the bestsoft magnetic properties, such as Bs=1.15T, Hc=0.9928A/m, μi=48460.Fe94-xZr2Nb4Bx(x=10,15,20at.%) supersaturated solid solution nanostructured powderswere produced by mechanical alloying. Results show that the addition of metalloid element B,did not improve the glass forming ability of the alloy system. By adding B to substitute Fe,the saturation magnetization (Ms) decreased from the161.70emu/g (x=10) to152.74emu/g(x=20), The saturation magnetization increased with increasing milling time and becameconstant at130h, but the coercivity (Hc) increased firstly and then decreased. The variation ofmagnetic parameters can be explained by Nano-scale effect and Herzer model. Fe84Zr2Nb4B10alloy after milled for130h and then annealed at650K for1h, which the coercivity decreasedfrom39.58Oe to11.74Oe and the saturation magnetization increased from161.70emu/g to163.75emu/g. The consolidated bulk sample exhibited a high relative density which reaches92%of the theoretical density and there was no phase change during SPS process, the saturation magnetization and susceptibility of the SPSed bulk sample improved in comparisonwith the annealed powders. Its saturation magnetization is182.53emu/g.Formation of Fe-Nb-X (X=Al, Zr, Ti, Ta) amorphous alloys from pure metal elements bymechanical alloying. Amorphous powders have a homogeneous distribution of elements andno obvious contaminants coming from MA. The mechanism of amorphization can beattributed to reaction within solid state. The crystallization of Fe-Nb-X (X=Al, Zr, Ti, Ta)amorphous powders proceeds through single reactions, having an obvious dynamic effect andstrong resistance to crystallization. With an increase in temperature, the effective activationenergy for crystallization increased firstly and then decreased. This achievement of the fullydensified bulk compacts is ascribable to the viscous flow of amorphous powders and thespecial sintering mechanism of SPS. With the increase of sintering temperature, the densityand microhardness of the SPSed compacts increased obviously. The sintered samplesexhibited typical brittle fracture characteristics under single-axis compressive test at roomtemperature due to the presence of porosity in sintered compacts.
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