Crystallization kinetics of (Ni0.75Fe0.25)78Si10B12 amorphous alloy

Amorphous ribbon specimen of (Ni_0.75Fe_0.25)₇₈Si₁₀B₁₂ has been prepared by a single roller melt-spinning technique in the air atmosphere. The crystallization kinetics of the alloy has been investigated using different thermal analysis by means of continuous heating and isothermal heating. The activation energy of the alloy has been calculated by using Kissinger plot method and Ozawa plot method based on differential thermal analysis data, respectively. The products of crystallization have been analyzed by X-ray diffraction. A single phase of γ-(Fe, Ni) solid solution with grain size of about 10.3 and 18.5 nm precipitates in the amorphous matrix after annealing at temperatures 715 and 745 K, respectively. The crystallized phases are γ-(Fe, Ni) solid solution, Fe₂Si, Ni₂Si, Fe₃B and unidentified phase after annealing at 765 K. The details of nucleation and growth during the isothermal crystallization are expatiated in terms of local Avrami exponent and local activation energy.     

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.     

Pressure-induced crystallization in a bulk amorphous Zr-based alloy

Crystallization of multi-component on amorphous Zr-based alloy (Zr₄₁Ti₁₄Cu_12.5Ni₉Be_22.5C₁) is investigated at different pressures and temperatures. We have previously found that the primary crystallization temperature decreases with increasing pressure below 6 GPa, and the crystallization follows a different process under high pressure when compared to that at ambient pressure. In this work, pressure-induced crystallization is observed by in situ X-ray diffraction (XRD) using synchrotron radiation in a diamond anvil cell at ∼25 GPa and room temperature. This phase transition between amorphous and crystalline is reversible and the crystallized sample returns to the amorphous state during decompression. The mechanism for pressure-induced crystallization is discussed. We suggest that the crystallized phases under high pressure are interstitial solid solution phases formed from the amorphous matrix without long-range atomic rearrangements.     

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.     

Crystallization of amorphous Cu60Zr40 prepared by magnetron sputter deposition

The crystallization of amorphous Cu₆₀Zr₄₀ prepared by magnetron sputter deposition was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. Calorimetric results were similar to those reported in the literature for liquid-quenched Cu₆₀Zr₄₀, including the manifestation of a glass transition. Crystallization above and below the glass transition temperature, T_g, occurred by nucleation and growth of the equilibrium phase, Cu₁₀Zr₇. This phase was characterized by convergent beam electron diffraction. With isothermal annealing below T_g, the time scale for crystallization indicated that the vapor-quenched alloy was kinetically more stable than the liquid-quenched alloy. This was interpreted as a difference in the quenched-in structures, produced by the different synthesis methods. During longer anneals, TEM analysis indicated that the structure was being contaminated by oxygen.     

A comparison of the crystallization behavior of liquid-quenched and vapor-quenched amorphous Cu60Ti40

The crystallization behavior of two Cu₆₀Ti₄₀ amorphous alloys, one prepared by a vapor-quench (VQ) process and one by a liquid-quench (LQ) process, has been studied using differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. Microstructural studies show that the two alloys have the same transformation sequence under similar annealing conditions. However DSC measurements of the crystallization temperature during isochronal annealing and of the incubation time for crystallization during isothermal annealing show that the LQ alloy is more thermally stable and therefore more structurally relaxed. TEM analysis of the partially annealed microstructures gives some insight into the mode of crystal nucleation and growth as a function of temperature. During isothermal annealing significant differences are observed for the two alloys in the shape and orientation of the crystals and in the crystal structure formed. Whereas the VQ alloy transforms polymorphicaly into the intermetallic Cu₃Ti₂, the LQ alloy forms the Ti-rich phase, Cu₄Ti₃. The two phases are closely related in structure and composition. The differences observed for the two alloys are discussed in terms of greater structural relaxation and short range order in the LQ alloy resulting from the mode of synthesis.     

Electron microscopic study of the crystallization kinetics of the amorphous alloy Pd80Si20

Amorphous Pd₈₀Si₂₀ foils, prepared by the rapidly rotating mill device method, were quenched from the liquid state, temperatures of the melt being 1100, 1500 and 1600°C. The foils were linearly heated at a rate of 1.5 °C/min over a temperature range of 20–600°C. The structural changes were observed by methods of optical microscopy, transmission electron microscopy and electron diffraction. The beginning of crystallization of the amorphous phase is affected by the temperature of the melt. The crystallization of the amorphous phase was terminated at a temperature of 390–400°C. Silicides Pd₉Si₂ and Pd₃Si, the morphology of which varied with temperature, were formed during crystallization.     

Zircon formation from amorphous powder and melt in the silica-rich region of the alumina–silica–zirconia system

Chemically homogeneous amorphous powders were prepared by sol–gel method from alkoxide mixtures in the silica-rich region of the alumina–silica–zirconia system. A glass with the same composition was obtained by quenching in water from the melt. The evolution with temperature in the range up to 1625 °C was studied by means of X-ray diffraction, infrared and UV-Raman spectroscopy, scanning electron microscopy and energy-dispersive X-ray analysis. Zircon crystallization and stability at temperatures higher than the liquidus temperature were confirmed in both melt-quenched and gel-glasses. Crystallization of cristobalite from the amorphous gel-glasses was observed above 1200 °C. The crystallization of zircon particles was observed after thermal treatment at 1550 °C. At 1625 °C zircon was the only stable crystalline phase due to the complete melting of the silica-rich matrix. The XRD pattern of the ternary gel treated at 1625 °C shows clearly the disappearance of the cristobalite phase, while at 1550 °C there is already partial melting. These results can help to determine the phase equilibrium in the ternary system.     

Specific features of sample preparation from amorphous aluminum alloys for transmission electron microscopy

An aluminum amorphous alloy doped with transition (Fe and Ni) and rare earth (La) metals has been used as an object of systematic study of the structural transformations that are characteristic of different methods of sample preparation for transmission electron microscopy (the mechanical tearing of ribbons, electrochemical thinning, and Ar⁺-ion etching under different conditions). The results of X-ray diffraction analysis and a calorimetric study of the structure in comparison with electron microscopy data made it possible to determine the optimal method of sample preparation, which ensures minimum distortions in the structure of metastable amorphous alloys with a low crystallization temperature.     

MeV electron irradiation induced crystallization in metallic glasses: Atomic structure,crystallization mechanism and stability of an amorphous phase under the irradiation

MeV electron irradiation via high voltage electron microscopy can lead to amorphous-to-crystal transition (i.e., crystallization) as well as crystal-to-amorphous transition (i.e., solid-state amorphization). Irradiation-induced crystallization can be observed in various alloy systems such as Co-, Fe-, Ni-, Pd-, and Zr-based metallic glasses, indicating that this phenomenon has wide generality in metallic materials. Irradiation-induced crystallization mechanism was discussed based on the following factors; (1) an increase in free energy for an amorphous phase, (2) the formation of crystalline clusters through modification of the atomic configuration near radiation induced defects, and (3) enhanced diffusion. The stability of an amorphous phase against irradiation-induced crystallization can be estimated from the thermal crystallization temperature (T_x), and Ni–Nb based metallic glasses have a tendency for high stability against irradiation because of high T_x.     

In situ energy dispersive X-ray diffraction analysis of the high-pressure–high-temperature stability of amorphous Co–Fe–Zr–B alloys

The pressure–temperature stability of Co₅₆Fe₁₆Zr₈B₂₀ amorphous alloys was investigated by energy dispersive X-ray diffraction. The in situ experiments were performed at the MAX80/F2.1 high-pressure beamline at the HASYLAB synchrotron radiation facility (Hamburg, Germany). Crystallization experiments were performed under different applied pressures up to 2 GPa. The effect of static pressure on the crystallization temperature stems from the pressure effect on the nucleation barriers and modified kinetics of solid-state diffusion under high-pressure–high-temperature conditions.     

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.     

The effect of high pressure on crystallization of splat-cooled V2O5

Crystallization of splat-cooled V₂O₅ under high pressure was examined. By X-ray diffraction and thermal analysis, it is shown that the non-crystalline V₂O₅ crystallizes dramatically up to about 6 kb. Crystallization temperature increases with increasing pressure under this pressure range.At higher pressure (20–60 kbar), crystallization occurs gradually and the crystallization temperature has a slight tendency to decrease with increasing pressure.     

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.     

Effect of Nb in the nanocrystallization and magnetic properties of FeNbBCu amorphous alloys

The crystallization of melt-spun Fe_79?xNb_5+xB₁₅Cu₁ (x = 0, 2, 4) ribbons has been studied by differential scanning calorimetry and X-ray diffraction. A primary crystallization of bcc-Fe nanoparticles embedded in an amorphous matrix, followed by the precipitation of metastable borides from the residual matrix at higher temperatures is observed. The characteristic temperatures of crystallization events change with Nb concentration. The results obtained from thermal and structural characterization are related to the magnetic properties of the sample. A dependence of the magnetic behavior with the Fe/Nb content in the alloy is also unveiled. The decrease of Nb content in the alloy leads to an enhancement of both the saturation polarization and the Curie temperature due to variations in the exchange coupling between Fe atoms. However, the maximum values of magnetic entropy change do not vary appreciably among the three amorphous alloys. In nanocrystalline samples the amount of the nanocrystalline transformed fraction seems to be the main reason for the change in the saturation polarization of the sample.     

Oxidation Kinetics of Amorphous,Polycrystalline, and Nanocrystalline Co33Zr67 Alloys

The oxidation kinetics of amorphous, polycrystalline, and nanocrystalline CoZr₂ alloys have been studied under isothermal conditions in air atmosphere with a microbalance. DSC and X-ray diffraction were used to study the influence of oxidation on crystallization. The three alloys under investigation which have the same composition but differ in the microstructure showed noticeable differences in their oxidation behaviour: the oxidation of the amorphous alloy is characterized by a very fast initial oxygen absorption step, completed in less than 1–2 min, followed by a slow oxide growth obeying a logarithmic time law at 400 °C. The polycrystalline thermodynamically stable tetragonal alloy absorbs small amounts of oxygen and obeys a parabolic rate law in the temperature range 500–800 °C. The activation energy of oxygen diffusion in tetragonal CoZr₂ was determined from the temperature dependence of the parabolic rate constant. The intermediate nano-crystalline phase with a local structure more closely packed and ordered than that of the precursor amorphous phase, shows an oxidation behaviour similar to that of the tetragonal phase, but with a different time exponent.     

Influence of outphase Cu50Ti50 amorphous alloy addition on microstructural evolution of mechanically alloyed Zr66.7Ni33.3 amorphous alloy

The influence of outphase Cu₅₀Ti₅₀ amorphous alloy addition on microstructural evolution of Zr_66.7Ni_33.3 amorphous alloy has been investigated using a mechanical alloying method. It has been found that the milling induced microstructural evolution is related to the change of peak positions of the first maximum on X-ray diffraction patterns of the as-obtained amorphous alloys. With increasing milling time, the 3 wt.% Cu₅₀Ti₅₀ addition can give rise to the cyclic amorphization transformation of the as-milled alloy. The mechanical stability of the mixing amorphous phase can be greatly enhanced with increasing Cu₅₀Ti₅₀ addition up to 10 wt.%. Moreover, the addition of outphase Cu₅₀Ti₅₀ amorphous alloy not only increases the onset crystallization temperature of Zr_66.7Ni_33.3 amorphous alloy but also alters its crystallization mode. The effect of outphase amorphous addition on the mechanical stability of the Zr_66.7Ni_33.3 amorphous phase has been discussed based upon the bond order theory.     

Crystallization of amorphous Al2O3–SiO2 precursors doped with nickel

The crystallization of amorphous diphasic Al₂O₃–SiO₂ precursors doped with nickel has been studied by differential scanning calorimetry (DSC), XRD diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Diphasic gels with constant atomic ratio (Al + Ni)/Si = 3:1, where 0, 1, 2 and 3 at.% of aluminum were replaced by nickel, have been prepared by hydrolyzing of TEOS in aqueous solution of aluminum nitrate. Crystallization of Ni-containing γ-Al₂O₃ preceded the crystallization of Al–Si spinel. Activation energy of 603 ± 16 kJ mol⁻¹ for crystallization of Ni-containing γ-Al₂O₃ was obtained in non-isothermal conditions. Ni-incorporated γ-Al₂O₃ transforms gradually with the temperature increase into Ni aluminate spinel, while Al–Si spinel reacts with amorphous silica forming mullite at about 1200 °C. Rietveld structure refinement of phases present in the samples annealed at 1600 °C and SEM-EDS and TEM-EDS analyses of related phases have shown that nickel predominantly crystallizes as NiAl₂O₄, but small amount of nickel is incorporated in mullite structure, as well as, dissolved in the glassy phase of the system.     

Phase transformation and crystallization kinetics of melt-spun Ni60Nb20Zr20 amorphous alloy

The glass transition and crystallization kinetics of melt-spun Ni₆₀Nb₂₀Zr₂₀ amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The dependence of glass transition and crystallization temperatures on heating rates was analyzed by Lasocka's relationship. The activation energies of crystallization, E_x, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics and the Avrami exponents are in the range of 1.92–2.47 indicating a diffusion-controlled three-dimensional growth mechanism. The activation energy obtained from the Arrhenius equation in the isothermal process was calculated to be E_x = 419.5 kJ/mol. The corresponding three dimensional (3D) time–temperature–transformation (TTT) diagram of crystallization for the alloy has been drawn which provides the information about transformation at a particular temperature. In addition, the intermetallic phases and morphology after thermal treatment have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM).