Nanocrystallization-induced structural evolution of intergranular amorphous phase in Fe78B13Si9 alloy

The nanocrystallization-induced structural evolution of the intergranular amorphous phase in a Fe₇₈B₁₃Si₉ alloy was investigated by X-ray diffraction (XRD) measurements, transmission electron microscopy (TEM), and positron annihilation spectroscopy. Crystallization occurs at 773 K, where nanocrystallites of α-Fe with an average grain size of a few tens of nanometers are formed in an amorphous matrix. With increasing annealing temperature up to 973 K, the average grain size increases up to ∼80 nm. In the as-prepared sample corresponding to an amorphous precursor, more than 90% of the positrons are localized at vacancy-sized free volumes dominantly surrounded by Fe atoms and other positrons are trapped by microvoids. Along with the appearance of nanocrystallites and their growth due to annealing, the concentration of microvoids is increased in the intergranular amorphous phase.     

Glass-to-crystalline transformation in rapidly quenched Fe78B9Si13 ferromagnetic alloy

Calorimetric studies of the ferromagnetic Curie temperature T_c, and the crystallization kinetics of the metallic glass Fe₇₈B₉Si₁₃ have been performed in an attempt to elucidate the possibility of reversible relaxation processes near T_c and the crystallization mechanisms taking place. From the change of T_c with heating rate and on annealing it appears that ageing irreversibly increases the Curie temperature. Crystallization is thermally activated following an Arrhenius behaviour and proceeds in two stages, the best fit to the experimental data for each stage of crystallization has been obtained by use of a Johnson-Mehl-Avrami-Erofe'ev equation. The effective activation energy and the kinetic exponent are respectively E = (4.7 ± 0.1) eV, n = 2.0 ± 0.2 for the first and E = (4.5 ± 0.1) eV, n = 4.0 ± 0.2 for the second stage of crystallization. From these results it appears that the mechanisms of crystallization are quite different in both stages.     

The use of flow behavior and thermal expansion to monitor structural change of amorphous Fe78Si9B13 ribbon

Samples of the amorphous Fe₇₈Si₉B₁₃ ribbon were annealed isothermally and isochronally under different tensile stresses. These samples were also investigated using thermal expansion tests, DSC and XRD methods. The results show that a structural transition similar to the glass transition was found using thermal expansion method. Comparing the XRD patterns of the tensile stress annealed samples with those of stress free annealed samples, it is suggested that tensile stress promotes the crystallization.     

Magnetic behaviors of amorphous Fe78Si9B13 thin films prepared by pulsed laser deposition

Amorphous magnetic thin films have been deposited onto BK-7 substrates using the pulsed laser deposition technique. The source material irradiated by the laser was a pack of amorphous ribbons of composition Fe₇₈Si₉B₁₃. The structural properties of thin films were investigated and a large number of droplets were observed in the magnetic layers. Electric current passing through the films causes significant deformation of droplets and consequently changes the magnetic thin films characteristics. Magnetic properties evolution after electrical processing was investigated using magneto-optical Kerr effect.     

Structural and dynamical properties of Fe78Si9B13 alloy during rapid quenching by first principles molecular dynamic simulation

Structural evolution of the Fe₇₈Si₉B₁₃ alloy during rapid quenching was investigated by ab initio molecular dynamics simulation. The second peak splitting has been perceived even at 1473 K in the partial pair correlation functions though not in the total pair correlation function. The (0, 3, 6, 0) polyhedra are abundant in the liquid state while the distorted (0, 3, 6, 0) polyhedra are the featured local structure around B atoms in the amorphous state. The diffusion coefficients of the three elements are evaluated to understand the dynamics of quenching. From 1173 to 873 K the three coefficients are coherent. We think this temperature range corresponds to the supercooled liquid region, and 873 K serves as the glass transition temperature.     

Ball milling induced abnormal crystallization behavior of an amorphous Fe78Si9B13 alloy

This paper investigates the effect of milling atmospheres on mechanical crystallization of an amorphous Fe₇₈Si₉B₁₃ alloy during ball milling. Under an air atmosphere, the amorphous alloy completely transforms into a single α-Fe(Si) phase after milling of 30 h. The crystallization process and products are different from those of thermal crystallization and milling induced crystallization under an argon atmosphere. Moreover, the milling atmosphere has a significant influence on the thermal crystallization of the amorphous phase in the as-milled alloy.     

Nanocrystallization and structure of Fe78.5Ni1.0Mo0.5Si6.0B14.0 amorphous alloy

The effect of Ni and Mo alloying additions on crystallization of an Fe–Si–B based amorphous alloy was studied by applying various experimental techniques – DSC, XRD and TEM. It was shown that both alloying additions Ni and Mo change the crystallization temperature as well as the activation energy of primary crystallization. The phases formed during primary crystallization for the Fe₈₀Si₆B₁₄ and Fe_78.5Ni₁Mo_0.5Si₆B₁₄ alloys were the same, however the morphologies were significantly different. The addition of 1.0 at.% of Ni and 0.5 at.% Mo changed the crystallization mechanism and the type of formed phases. Such additions also resulted in formation of nanocrystals. The kinetic and thermodynamic characteristics of annealed specimens of amorphous metallic Fe₈₀Si₆B₁₄ and Fe_78.5Ni₁Mo_0.5Si₆B₁₄ alloys were established. These characteristics were determined based on measurements of instantaneous changes of electrical strength. It was shown that the method of electromotive force measurements was more sensitive to structural changes and the phase composition of amorphous metallic electrodes in comparison with the X-ray method.     

Magnetostatic properties of amorphous and nanostructured Fe73.5Si13.5B9Cu1Nb3 wires

We present the results of experimental investigations of magnetostatic properties of Fe-based amorphous wires with diameter about 100 μm. The samples were annealed at different conditions. The as-quenched sample had a weak increase (about 5%) of the magnetization with magnetic field decrease – the negative differential magnetic permeability could be observed in its hysteresis loops. The coercive force was about 0.2 Oe. The conventional annealing decreased the value of the saturation field down to 5 Oe without change of the coercive force value. When the annealing was accompanied with torsion stress the coercive force became less than 50 mOe. After the current annealing any peculiarities disappeared in magnetization in a weak magnetic field.     

Structural behavior of amorphous and liquid metallic alloys at elevated temperatures

The thermal behavior of the short-range order of Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glasses has been investigated in situ by means of high-temperature X-ray synchrotron diffraction. The dependence of the X-ray structure factor S(q) of the glassy state on temperature follows the Debye theory up to the glass transition. Above the glass transition temperature T_g, the temperature dependence of S(q) is altered toward a continuous development of structural changes in the liquid state with temperature. The behavior of the structure factor during heating and cooling through the glass transition gives experimental evidence for melting the glass, and for freezing the liquid, respectively at the caloric glass temperature.     

Dynamic deformation of silicon-rich V3Si single crystals at elevated temperatures

The plastic deformation behaviour of the intermetallic phase V₃Si (Cr₃Si type) was investigated under dynamic conditions. The experiments revealed that V₃Si deforms plastically at a strain rate of about 4.7 × 10⁻⁵s⁻¹ above 1200°. Flow stress depends strongly on deformation temperature and strain rate. An alloy hardening by deviation from stoichiometric composition within the range of homogeneity is observed.     

Improved tensile ductility of amorphous Fe78Si9B13 alloy using electrodeposited nano-Ni layers

In order to improve the tensile ductility of amorphous Fe₇₈Si₉B₁₃ alloy, nano-Ni layers were electrodeposited on the amorphous alloy ribbon and amorphous Fe₇₈Si₉B₁₃/nano-Ni laminated composite was prepared. The tensile ductility of laminated composite and monolithic amorphous alloy at both room and high temperatures was examined. The elongation of the amorphous Fe₇₈Si₉B₁₃ alloy and that in the laminated composite increases from 1.4% to 8.5% and from 36.3% to 115.5% at room temperature and 450 °C, respectively. The improved tensile ductility using electrodeposited nano-Ni layers is attributed to a good bonding between the amorphous Fe₇₈Si₉B₁₃ layer and nano-Ni layers. The amorphous layer can deform in conformity with Ni layers and be significantly stretched without fracture.     

Effect of Al substitution on the magnetic properties of amorphous Fe73.5Cu1Mo3Si13.5−xAlxB9 alloy

We have synthesized FINEMET type amorphous Fe_73.5Cu₁Mo₃Si_13.5−xAl_xB₉ alloy by the single wheel melt spinning technique. The effect of Al substitution on the magnetic properties has been studied using a vibrating sample magnetometer, SQUID and Mössbauer spectroscopy. Magnetization and Curie temperature of the amorphous phase of the alloys were found to decrease with Al concentration. The results are attributed to the dilution effect of Al on the magnetic moment of Fe and to the increase in Fe–Fe interaction distance resulting in the weakening of exchange interaction.     

Low temperature electron irradiation of amorphous and crystalline FeB alloys

Three amorphous FeB based alloys and crystalline Fe₃B alloy were irradiated at a temperature of 21 K with 2.5 MeV electrons. The irradiation induced increase of electrical resistivity (Δ?) was measured during irradiation. the damage produced was analysed with the conventional production curve $\text{Δ}\text{dot}\text{?}\text{=}\text{d}\text{(Δ?)/}\text{d}\text{(?t)}$ versus Δ? where ?t is the electron dose. After irradiation, isochronal annealings were performed up to room temperature. The behaviour of the four alloys was found to be similar both during irradiation and annealing.For all the alloys: the production curve is linear at high doses; and the induced increase of electrical resistivity Δ? anneals out at low temperature following different stages. These results are interpreted in terms of the creation of well defined defects.These defects have the same nature in amorphous and crystalline alloys; i.e. probably of vacancy type.     

Ultrasonic studies of the amorphous binary alloy Pd0.82Si0.18 at low temperatures

Ultrasonic attenuation and velocity changes are measured in an amorphous Pd_0.82Si_0.18 binarys alloy at frequencies from 10 MHz to 200 MHz (transverse) and temperatures down to 0.27 K. The attenuation is found to contain an amplitude dependent (saturable) component. These observations, as well as the temperature dependence of the velocity changes, are consistent with the predictions of the two level tunnelling systems (TLS) theory. Contrary to the predictions of this theory, however, linear frequency dependence and essentially no temperature dependence of saturable attenuation changes were observed at very low temperatures.     

In-situ crystallization of amorphous Fe73−xNbxAl4Si3B20 alloys through synchrotron radiation

In the present work Fe_73−xNb_xAl₄Si₃B₂₀ (x = 5, 10) alloys have been processed by melt-spinning with the aim of studying the crystallization sequence through annealing in suitable temperatures. Melt-spun ribbons were characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) through Cu-Kα (λ = 1.54 Å) and synchrotron radiation (λ = 1.77 Å) and transmission electron microscopy (TEM). Soft magnetic properties were measured through the hysteresis loop tracer. In-situ XRD through synchrotron radiation was very accurate in phase identification. Fe_73−xNb_xAl₄Si₃B₂₀ (x = 5, 10) alloys showed the possibility of forming ferromagnetic amorphous alloys composed of commercial Fe-based master alloys with fine nanocrystalline structure and good soft magnetic properties.     

Study of characteristics of plastic deformation in amorphous Fe-Cr-Mo-V-B-Si alloy by the method of local deformation

Characteristics of plastic deformation in the amorphous Fe-Cr-Mo-V-B-Si alloy have been studied by the method of local deformation. It is established that plastic deformation in the rapidly quenched iron-based alloy proceeds by two channels. The model for interpreting the energy aspects of plastic deformation in amorphous materials is suggested.     

Electrical resistivity evolution in the annealed amorphous Fe78Si9B13 ribbons

The electrical resistivity was measured at room temperature for the amorphous Fe₇₈Si₉B₁₃ ribbons annealed at various temperatures for different holding time. Although the annealed Fe₇₈Si₉B₁₃ ribbons are in full amorphous state, their electrical resistivity obviously varies with the annealing time. At every annealed temperature, the electrical resistivity evolution can be divided into regions I, II, and III, respectively. Using X-ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we investigated the ribbons overlapping regions I and II (called the focused ribbons, FRs). The results show that the change of electrical resistivity, fracture morphology, thermal effect in DSC analysis of the focused ribbons (FRs) can be ascribed to the evolution of the short range order (SRO) in the amorphous alloy.     

The structure and properties of nanocrystalline Fe78B13Si9 alloy

A new method has been employed to prepare a nanocrystalline alloy from amorphous ribbons and some of the structure-dependent properties of this alloy have been studied and compared with those of coarse-grained crystalline and amorphous FeBSi alloys. The new method of preparing nanocrystalline alloys involves annealing isothermally an amorphous ribbon of the same composition. By comparing the structure-dependent properties, it can be concluded that the novel properties of the nanocrystalline alloy reflect the unusual nature of its grain boundaries.     

Crystallization of metastable phases in the Pd83Si17 amorphous alloy

The crystallization of the Pd₈₃Si₁₇ amorphous alloy started by formation of small crystallites. By comparisons of selected area electron diffraction patterns from the crystallites and patterns calculated from generated models we found that the first observed structures coincide with long range vacancy ordered structures derived from CsCl-type structure, known as τ-structures. The Pd atoms are in the corners and the Si atoms or vacancies are in the centers of basic cubic cell, respectively. It is possible to interpret the formation of these transition structures as consequence of occurrence of small areas with different chemical composition present in original amorphous structure as a result of rapid quenching. After ageing the τ-structures transform by diffusion to the stable Pd₉Si₂ structure.