Crystallization behavior,mechanical properties,and corrosion resistance of an amorphous Fe<Subscript>76.5</Subscript>P<Subscript>13.6</Subscript>Si<Subscript>4.8</Subscript>Mn<Subscript>2.4</Subscript>V<Subscript>0.2</Subscript>C<Subscript>2.5</Subscript> alloy

We have studied the mechanical properties and corrosion resistance of an amorphous Fe_76.5P_13.6Si_4.8Mn_2.4V_0.2C_2.5 alloy and their response to nanocrystallization as a result of brief lamp processing and heat treatment. The results demonstrate that the lamp processing time needed to obtain a given phase composition through partial crystallization of the amorphous alloy is two orders of magnitude shorter than the corresponding heat treatment time. We have found lamp processing conditions that ensure the formation of an amorphous–nanocrystalline composite with a twofold increase in hardness, without loss of plasticity. It has been shown that, with increasing loading rate during nanoindentation, the hardness of the alloy decreases because of the increase in plasticity, which shows up as the formation of a larger number of shear bands. Under uniaxial tension, the material exhibits microplasticity, which may be due to intercluster sliding, with the amorphous structure retained. The corrosion resistance of the as-prepared amorphous alloy in a medium contaminated with sulfur dioxide exceeds that of the partially crystallized alloys.     

Structural and morphological properties of Fe2O3/TiO2 nanocrystals in silica matrix

We report on structural, morphological and ordering properties of Fe₂O₃/TiO₂ nanoparticles embedded in SiO₂-based multilayers. We investigated the structure of these systems by X-ray diffraction and grazing incidence small angle X-ray scattering after post-growth annealing. We found that the presence of TiO₂ promotes the growth and crystallization of the nanocrystals of Fe₂O₃. In multilayers containing both Fe₂O₃ and TiO₂, crystalline nanoparticles create partially ordered three-dimensional arrays.     

Crystallization behaviour and mechanical properties of rapidly solidified Al<Subscript>87.5</Subscript>Ni<Subscript>7</Subscript>Mm<Subscript>5</Subscript>Fe<Subscript>0.5</Subscript> amorphous alloy

The crystallization behaviour and the mechanical properties of rapidly solidified Al_87.5Ni₇Mm₅Fe_0.5 alloy ribbons have been examined in both as-melt-spun and heat-treated condition using differential scanning calorimetry, X-ray diffractometry (XRD), transmission electron microscopy (TEM), tensile testing and Vicker’s microhardness machine. XRD and TEM studies revealed that the as-melt-spun ribbons are fully amorphous. The amorphous ribbon undergoes three-stage crystallization process upon heating. Primary crystallization resulted in the formation of fine nanocrystalline fcc-Al particles embedded in the amorphous matrix. The second and third crystallization stages correspond to the precipitation of Al₁₁(La,Ce)₃ and Al₃Ni phases, respectively. Microhardness and tensile strength of the ribbons were examined with the variation of temperature and subsequently correlated with the evolved structure. Initially, the microhardness of the ribbon increases with temperature followed by a sharp drop in hardness owing to the decomposition of amorphous matrix that leads to formation of intermetallic compounds     

Non-equilibrium crystallization diagram for the Co75.26−xFe4.74(BSi)20+x amorphous metal alloys

A non-equilibrium crystallization diagram for Co sub-surface layers of the Co_75.26–x Fe_4.74(BSi)_20+x amorphous alloy for x > 1 during magnetic field annealing is determined using Transmission Electron Microscopy (TEM). The diagram shows that, depending on the composition and temperature, the Co sub-layer exhibits five distinctively different microstructures when the metallic glass is heat treated below its bulk crystallization temperature. At high boron content, the structure is dominated by the FCC structure with a high degree of oxygen impurity faulting regardless of the annealing temperature. At low concentration, the Co sub-layer exhibits FCC or HCP structures, depending on the temperature. Also found was a two-phase region in which FCC and HCP Co co-existed. Such a diagram serves as a useful guide to obtaining the desired properties as the microstructure is closely linked to the magnetic properties of the material.     

Highly amorphous Fe90Zr10 thin films, and the influence of crystallites on the magnetism

A method for depositing highly amorphous, iron-rich Fe_100 − xZr_x thin films on to room temperature substrates is presented. The method involves co-depositing Fe and Zr on to an amorphous AlZr layer. Experimental proof that the structures are completely amorphous is given by transmission electron microscopy and polarized neutron reflectometry. The reflectometry measurements also give an indication of the impact that Fe crystallite impurities have on the magnetic structure and properties of amorphous FeZr. The results are consistent with previous investigations on bulk samples, which showed that crystalline impurities make the magnetic structure more non-collinear.     

Conversion electron Mössbauer spectroscopy of the surface crystallization of the Fe75Co9B16 amorphous alloy

Using a new design of helium-methane gas-flow detector of conversion electrons for Mössbauer spectroscopy, non-uniform nucleation of the primary -Fe-Co phase on both contact and free surfaces of the Ar(+H₂) annealed amorphous Fe₇₅Co₉B₁₆ alloy was observed in its early crystallization stage. In this state the amount of crystalline phase on the contact ribbon side surpasses that on the free one by a factor of three, whereas no traces of volume crystallization were observed in the transmission spectra. By applying ion implantation to both ribbon surfaces, a slight reduction of the crystalline phase contribution was found. Magnetic domain structure observations were performed in order to evaluate the influence of surface crystallization on magnetic properties.     

Structural modification and phase transformation kinetics: crystallization of amorphous Fe40Ni40P14B6 eutectic alloy

The effect of processing histories (fluxing and pre-annealing) on the amorphous structure and the crystallization kinetics of amorphous Fe₄₀Ni₄₀P₁₄B₆ alloy prepared by melt spinning has been studied by differential scanning calorimetry, X-ray diffraction, transmission and scanning electron microscopy. For isothermal crystallization, an incubation time exists, and for isochronal crystallization, an abnormally sharp crystallization peak (with the transformed fraction corresponding to the transformation-rate maximum f _p as less than 0.632) occurs. Subjected to fluxing and pre-annealing, the incubation time (in isothermal crystallization) decreases, whereas the initial crystallization temperature (in isochronal crystallization) declines as well as the less sharp crystallization peak and f _p approaches 0.632. A kinetic model considering transient nucleation is proposed and analyzed, which could describe well the singular crystallization behavior of amorphous Fe₄₀Ni₄₀P₁₄B₆ alloy. A recipe based on the kinetic model is also proposed to obtain the kinetic parameters from experiment data. Via kinetic analysis and amorphous structural characterization, it is considered that pre-annealing and fluxing promote relaxation of the system close to the meta-stable equilibrium state; the atomic structure becomes more similar to the correspondingly crystallized phase, thus declining the amorphous stability and alleviating the transient effect on nucleation.     

Effect of Crystallization on the Electrical Resistance and Structure of the Co67Cr7Fe4Si8B14 Amorphous Alloy

The variations in the electrical resistance and structure of amorphous Co₆₇Cr₇Fe₄Si₈B₁₄ during constant-rate heating were studied by four-probe ac measurements and x-ray diffraction. The crystallization process was shown to follow the eutectic mechanism. The phase composition of the crystallization products was determined. Between 870 and 920 K, the alloy is in an amorphous–nanocrystalline state. The resistance of the as-prepared, amorphous alloy shows anomalies at about 497 and 843 K, which are interpreted in terms of structural changes.     

The interfacial structure of nanocrystalline Fe73.5Cu1Mo13Si13.5B9 studied by Mössbauer spectroscopy

Nanocrystalline Fe_73.5Cu₁Mo₃Si_13.5B₉ prepared by crystallization of the amorphous alloy was investigated by using Mössbauer spectroscopy and X-ray diffractometry. The present study focuses on the interfacial composition and the important role of the interfacial component in the development of the nanocrystalline structure. On the basis of a newly developed fitting program, the amorphous phase is denoted by a low field component and a high field one. Upon crystallization, the former, which corresponds to the boundary regions adjacent to the grains become more significant. The different stages associated with the crystallization are discussed.     

Formation of nanocrystalline structure during electron irradiation induced crystallization in amorphous Fe-Zr-B alloys

Effect of electron irradiation on the crystallization and phase stability of Fe₈₈Zr₉B₃ and Fe₇₁Zr₉B₂₀ amorphous alloys was examined. Electron irradiation at an accelerated voltage of 2000 kV was performed at room temperature. The Fe₇₁Zr₉B₂₀ alloy showed a wide supercooled liquid region and the ΔT_x value was 71 K, while no glass transition was observed in Fe₈₈Zr₉B₃ alloy. The amorphous phase in Fe–Zr–B alloys was not stable under irradiation and crystallization from the amorphous phase was accelerated by the irradiation. Nanocrystalline structure composed of α-Fe and cubic-Fe₂Zr was formed in Fe₈₈Zr₉B₃ alloy by irradiation induced crystallization, while no nanoscale precipitates of intermetallic compounds were formed during annealing. In Fe₇₁Zr₉B₂₀ alloy, the formation of nanocrystalline precipitates was also confirmed by irradiation induced crystallization, although the formation of nanocrystalline structure had not been realized in high B concentration Fe–Zr–B alloys by annealing. These new results show that electron irradiation is effective in producing a new nanocrystalline structure.     

Structure and properties of polyethyleneterephthalate crystallized by annealing in the highly oriented state

The structure of polyethyleneterephthalate bristles drawn about five times in the amorphous state and subsequently crystallized at temperatures between 100 and 260‡ C has been studied by means of small-angle X-ray scattering. In addition density, heat of fusion and wide-angle scattering behaviour were measured. For comparison, similar experiments were carried out with undrawn samples. The results showed that the degree of crystallinity of PET cannot be calculated from density data on the basis of a simple two-phase model, since the effective densitiesρ _c ^* andρ _a ^* of the crystalline and amorphous regions depend strongly on crystallization and drawing conditions. With rising crystallization temperature the size of the mosaic blocks building up the crystalline layers and their longitudinal mutual order increase whereas the volume fraction of the crystalline region is only rather slightly effected by the annealing temperature. The difference between the effective densityρ _c ^* and the “X-ray density”ρ _c of the crystalline layers is supposed to be caused by lattice vacancies in the boundaries of the mosaic blocks.     

Effect of the addition of Fe2O3 and heat treatment duration on the magnetic susceptibility of V2O5-P2O5-B2O3 glass system

The effect of the addition of Fe₂O₃ and heat treatment duration on the magnetic susceptibility of vanadium borophosphate glass were studied. The magnetic susceptibility of glass samples was found to increase with increasing Fe₂O₃ content, which may be explained by the formation of the FeO₆ group and the change of Fe²⁺ to Fe³⁺ which has higher paramagnetic properties. No detectable changes in the magnetic susceptibility with heat treatment for the samples containing 0.0, 0.5 and 1.0 mol% Fe₂O₃ was observed. The magnetic susceptibility for the heat treated samples containing 2.5, 5.0 and 7.5 mol% Fe₂O₃ decreases sharply with increasing duration of heat treatment up to 6 h and then remains almost constant. The sharp decrease in magnetic susceptibility of 2.5 mol% Fe₂O₃ is attributed to the increase in the number of ferrous ions. The sharp decrease for samples containing 5.0 and 7.5 mol% Fe₂O₃ is attributed to the increase in the number of Fe³⁺ in tetrahedral co-ordination. The rate of crystallization owing to the heat treatment was calculated and was found to increase with increasing iron oxide content. The geometry of crystallization was found to be in three-, two-and one-dimension(s) for samples containing 2.5, 5.0 and 7.5 mol% Fe₂O₃, respectively.     

Fast amorphization and crystallization in Al-Fe binary system by high-energy ball milling

Large amount of amorphous phase of Al-Fe binary system was obtained by MA of elemental powders using a high-energy ball mill at milling intensity of 150G (G is the gravitational acceleration). XRD, HRTEM and DSC were used to analyze the process of amorphization and crystallization. The time required achieving almost complete amorphous state is only 4.2 ks for Al-25 at.%Fe system and 3 ks for Al-30 at.%Fe system, respectively. The time of amorphous formation is very shorter than that of previous reports on Al-Fe binary system. Further milling causes rapid crystallization of the amorphous phase. By analysis of S(Q), the presence of a strong Al-Fe chemical short-range order in the amorphous matrix is suggested. Moreover, the superstructure of these Al-Fe clusters in the amorphous matrix is similar to the solid structure of Al₅Fe₂, and the clusters transform into the nucleus of Al₅Fe₂ intermetallic compound under the action of milling energy.     

Crystallization of Fe-P amorphous alloys as studied by the EDXD method

The crystallization of amorphous Fe-P alloys, made by electrodeposition, were studied using energy dispersive X-ray diffraction (EDXD), thermomagnetic, and Mössbauer measurements. EDXD proved to be especially useful, because its very short exposure time enabled us to perform isothermal crystallization measurements with practically continuous control by means of diffraction spectra. By measuring the intensity of the appropriate diffraction lines, the crystallization kinetics of each phase could be recorded simultaneously. At 610 K the crystallization of an Fe_81.2P_18.8 amorphous alloy was found to start within 5 min with the primary crystallization ofα-iron. This step is followed by the eutectic crystallization of the stable phasesα-iron and Fe₃P.     

Bulk nanocrystalline Al85Ni10La5 alloy fabricated by spark plasma sintering of atomized amorphous powders

Amorphous Al₈₅Ni₁₀La₅ powders were consolidated to cylindrical samples by spark plasma sintering (SPS), and their microstructures and mechanical properties were investigated. When the powders were consolidated below the crystallization temperature, an amorphous phase was retained in the consolidated sample. Sintering above the crystallization temperature caused full crystallization. The Vickers hardness of the amorphous-containing sample was about 350 HV in the as-sintered state and increased up to 450 HV by a subsequent heat treatment just below the crystallization temperature. The highest hardness was achieved in a nanocrystalline microstructure. Compression tests revealed the brittle nature of the consolidated samples although the fracture and yield strength was higher than 1 GPa. The brittleness is due to the low relative density of the amorphous-containing samples and the presence of a large amount of intermetallic compounds in the fully crystallized sample.     

Crystallization kinetics of the amorphous alloy Fe80B20 studied using a thermomagnetic balance

The kinetics of isothermal crystallization of the amorphous metal alloy Fe₈₀B₂₀ have been studied using a Perkin-Elmer thermomagnetic balance. Well-defined and reproducible incubation periods were observed on the degree of crystallization against time curves, in agreement with the theory of non-steady state nuclear ions in glasses. Values from 1.4 to 2.4 were obtained for the exponentn in the Johnson-Mehl-Kolmogorov-Avrami equation. The activation energy of viscous flow in the glass was found from the incubation period against temperature dependences at temperature near the crystallization point. The activation energy of crystallization was determined from the temperature dependence of the 50% crystallization times. Metallographic observations show unambiguously that two crystallization reactions proceed simultaneously: the growth of ready athermal centres located on the more slowly quenched surface of the amorphous metal ribbon along two directions, and growth in the bulk of the ribbon.     

Amorphous phase formation in Al80Fe10M10 (M?=?Ni, Ti, and V) ternary systems by mechanical alloying

In this study, the amorphous phase formation in Al₈₀Fe₁₀M₁₀ (M = Ti, V, Ni) (at.%) ternary systems during mechanical alloying has been investigated. The milled samples were characterized using X-ray diffraction and differential thermal analyses. A thermodynamic analysis of the amorphous phase formation was performed for these systems using the Miedema model. The obtained results demonstrate that amorphous phases can be formed during the mechanical alloying process of the Al₈₀Fe₁₀M₁₀ (M = Ti, V, Ni) ternary systems. The produced amorphous alloys exhibit one-stage crystallization during heating, which is amorphous to the Al₁₃Fe₄ intermetallic phases. The thermal stability of the produced amorphous phases decreases in the order of Al₈₀Fe₁₀Ti₁₀ > Al₈₀Fe₁₀Ni₁₀ > Al₈₀Fe₁₀V₁₀.     

Structural evolution of the Ti70Ni15Al15 powders prepared by mechanical alloying

Amorphization and crystallization behaviors of Ti₇₀Ni₁₅Al₁₅ powders during mechanical alloying (MA) and subsequent heat treatments are studied. Amorphous phase that cannot be obtained in the rapidly quenched ribbon is formed in the powders after MA for 60 h. Upon continuous heating of the amorphous powders in DSC, two exothermic events are observed. The first exothermic event corresponds to the crystallization of the amorphous matrix into a supersaturated α-Ti phase of hexagonal close-packed structure. The growth kinetic of the α-Ti phase is sluggish, resulting in the formation of nanostructured α-Ti matrix. The second exothermic event corresponds to the solid state transformation of the meta-stable α-Ti into the equilibrium phases, Ti₂Ni and Ti₃Al. Using the amorphous powders, Ti-based bulk materials with novel microstructures can be developed for structural applications.     

A jelly-like ceramic fiber at 1193 K

A high-strength ceramic Al₃₁Gd₉O₆₀ continuous fiber with a fiber diameter of about 20 μm and an amorphous structure could be made successfully by using the melt extraction method. This fiber can be freely shaped by viscous flow deformation in the supercooled liquid state (about 1193 K). The fiber strength is about 2 GPa and this strength is maintained up to around 973 K. A high-strength ceramic continuous fiber with a uniform GdAlO₃ nanocrystalline in an amorphous matrix can also be obtained with a suitable crystallization from the amorphous state by heat treatment. The heat resistance, Young’s modulus, and other properties are therefore improved. The amorphous ceramic fiber is promising as a ceramic that can be easily shaped at a relatively low temperatures (around 1193 K) in agreement with temperature range of superplastic processing of Ti alloys. Received: 25 August 1999 / Reviewed and Accepted: 28 October 1999     

Synthesis and characterization of Fe–B nanoparticles for potential magnetic applications

The crystallization and structure of Fe–B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe₈₀B₂₀ targets were analyzed by transmission electron microscopy. It is concluded that all NPs are covered by an amorphous Fe–B shell while the crystal structure of the NPs core depends on their size. Large NPs with diameters ≥30 nm are monocrystalline tetragonal Fe₃B, small diameter NPs (≤20 nm) are completely amorphous whereas in middle size NPs, with diameters between 20 and 30 nm, difference Fe–B phases (tetragonal Fe₃B and orthorhombic FeB) together with defaulted areas are observed. This work opens new possibilities to produce Fe–B NPs tailoring their magnetic properties by controlling their size and composition.