Induced crystallization of an amorphous Cu-Zr alloy

The crystallization behaviour of the amorphous Cu₆₀Zr₄₀ has been examined by simultaneous deformation and annealing, just below the crystallization temperature T_c. This treatment causes a heterogeneous nucleation and growth of small crystals, belonging to the Cu₁₀Zr₇ phase near the Cu₆₀Zr₄₀ composition. It was also found that subsequent annealing at temperatures $\text{T}\text{≤}\text{T}{}_{\mathrm{<mtext>c</mtext><mtext>?</mtext>}}$ does not accelerate the crystal growth, but results in a copious nucleation surrounding the single crystals.     

Characterization of crystallization in amorphous 2605 SC alloy

The annealing characteristics, the crystallization sequence of precipitating phases and their geometry have been studied for the amorphous alloy 2605 SC through X-ray and reflection electron diffraction, scanning electron microscopy and field ion microscopy.The as-received samples were found to contain small domains of crystalline Fe₃Si, Fe₂₃(B, C)₆ and an oxide of iron (maghemite, Fe₃O₄) on the ribbon surfaces.Samples annealed at 673 K for 10, 50, 100 and 1000 min reveal that there is a sequential difference in the crystallization of the ribbon surfaces and the bulk, the latter exhibiting the nucleation of α-Fe first. Moreover, in situ (in an electron microscope) continuous annealing of the samples indicates that, although formation of ferrite crystals occurs in the bulk, the initial crystallizing phase on the surfaces is the f.c.c. Fe₂₃(B, C)₆. Heat treatment at temperatures above 773 K, however, is seen to produce similar phase consistency, and thus diffraction patterns, from both regions. These structures primarily are seen to be composed of a dendritic α-Fe and the Fe₂₃(B, C)₆ phases along with the as yet non-crystallized amorphous domains. The equilibrium Fe₂B phase is not observed at the annealing temperatures (above 923 K) used.     

Kinetics of crystallization of a Fe-based multicomponent amorphous alloy

The Fe-based multicomponent amorphous alloys (also referred to as metallic glasses) are known to exhibit soft magnetic properties and, it makes them important for many technological applications. However, metallic glasses are in a thermodynamically metastable state and in case of high temperature operating conditions, the thermally activated crystallization would be detrimental to their magnetic properties. The study of crystallization kinetics of metallic glasses gives useful insight about its thermal stability. In the present work, crystallization study of Fe₆₇Co₁₈B₁₄Si₁ (2605CO) metallic glass has been carried out using differential scanning calorimetry (DSC) technique. Mössbauer study has also been undertaken to know the phases formed during the crystallization process. The alloy shows two-stage crystallization. The activation energy has been derived using the Kissinger method. It is found to be equal to 220 kJ/mol and 349 kJ/mol for the first and second crystallization peaks, respectively. The Mössbauer study indicates the formation of α-(Fe, Co) and (Fe, Co)₃B phases in the alloy.     

Zr对Pr-Fe-B非晶合金晶化形成纳米晶合金的作用

从非晶合金化激活能的角度，分析了Pr-Fe-B非晶合金在退火过程中晶粒粗大的原因，揭示了Zr元素在其晶化过程中的作用，结果表明，Zr能改变Pr-Fe-B非晶合金中α－Fe相的晶化行为，有助于形成尺寸细小的α-Fe相。     

Kinetics of thermal devitrification (crystallization) of a titanium amorphous alloy

Thermal investigation, by differential scanning calorimetry, of the behaviour of an amorphous alloy (39 Cu, 8 Ni, 1 Si and 52 Ti, wt%) was undertaken in a hydrogen atmosphere. It was shown that crystallization (devitrification) proceeds through four different stages within the temperature range 673 to 853 K (400 to 580° C) and consequently four exothermal maxima at temperatures which depend on the heating programme are registered on the thermograms. The activation energies of each cyrstallization stage, the frequency factor, rate constant, half-time of the reaction and crystallization enthalpy, were determined. Particular attention is paid to a discussion of the crystallization process of each stage in correlation with the results obtained by X-ray analysis.     

Nanolamellar structure obtained by simple crystallization of an amorphous cobalt-based magnetic alloy

A novel modulated nanolamellar structure with a lamellar spacing of about 5 nm was obtained by simple heat treatment of an initially amorphous Co/sub 65/Si/sub 15/B/sub 14/Fe/sub 4/Ni/sub 2/ magnetic alloy. The crystallographic characteristics of this nanolamellar structure were investigated using selected area diffraction pattern, Kikuchi maps, convergent beam electron diffraction, and X-ray diffraction techniques. The crystal structure of the lamellae was found to be a novel phase with a C-base centered orthorhombic crystal structure of a=0.74 nm, b=1.07 nm, and c=0.77 nm, the nanolamellar structure was modulated along the (0 0 1) plane. High-resolution transmission electron microscopy observations showed negligible lattice mismatch between neighboring lamellae. Electron energy loss spectroscopy mapping showed a periodic variation of boron composition corresponding to the nanolamellar periodicity. The formation of the nanolamellar structure was found to be due to spinodal decomposition within the grains formed by crystallization of the alloy.     

Isochronal crystallization kinetics of Fe40Ni40B20 amorphous alloy

The kinetics of crystallization of amorphous Fe₄₀Ni₄₀B₂₀ alloy upon isochronal annealing was investigated applying power-compensating differential scanning calorimetry with heating rates of (5, 10, 20, 30, 40) K/min. The corresponding microstructural evolution was studied by means of X-ray diffraction, focused ion beam and scanning electron microscopy, and transmission electron microscopy. Crystallization of Fe₄₀Ni₄₀B₂₀ alloy upon isochronal annealing takes place by formation of nano-scaled grains consisting of a face-centered cubic solid solution phase (Fe,Ni) and an orthorhombic compound phase (Fe,Ni)₃B. Kinetic analysis was performed by application of a modular model of phase transformation kinetics, fitted to all experimental transformation-rate curves simultaneously. The crystallization reaction can be described by nucleation with a continuous nucleation rate incorporating a nucleation index a and by growth in three dimensions according to a linear growth law. The kinetics of transformation and the resulting microstructure observed upon isochronal annealing clearly differ from those upon isothermal annealing investigated in a previous study, reflecting different mechanisms operating upon isochronal and isothermal crystallization.     

The formation and crystallization of an amorphous phase in an iron-carbon alloy

Splat-cooled foils of a carburised high purity Fe-C alloy have been examined by transmission electron microscopy. The crystalline phases that arose with an Fe¯4.3 wt % C amorphous phase on quenching and those that nucleated from the amorphous phase on heating were identified. The former was the HCP solid solution-phase whereas the latter, termed MS-I and MS-II, developed via two independent reactions yielding single phase ferrite grains and generally ferrite plus cementite grains, respectively. These observations have been interpreted in terms of the relative dispositions of transformation curves of the various metastable crystallization products.     

Phase diagram study of the formation and crystallization of Ge-metal amorphous alloy films

The Ge-Au and Ge-Ag alloy films were deposited in vacuum at room temperature and then systematically observed in the TEM. The maximum metallic concentrations in the alloy films,C _max, which form the stable amorphous alloy phases of germanium with gold and silver, were obtained. The annealed crystallization temperatureT _c, which falls with increasing metallic content in these films was also found. The structures of these films and their annealed specimens were also studied. There are various factors which influence the formation of amorphous alloy films deposited in vacuum for Ge-metal systems. A new formula forC _max has been derived. The annealed crystallization character has been explained by means of the variation of the free energy and the activation energy of crystallization. The activation energy of crystallization,E _a, can be obtained from the data values ofT _c. For Ge-Au films,E _a (Au)=E _a ^o /(–18.66C _Au ² +16.83C _Au+1)±3.3 (kcal mol^–1); for Ge-Ag films,E _a (Ag)=E _a ^o /(–2.754C _Ag ² +3.815C _Ag+ 1)±2.6 (kcal mol^–1). In order to explain all these results, two kinds of phase diagram for the alloy films have been introduced. One is the three-dimensional relationship diagrams of phase formation in semiconductor-metallic alloy films; it was introduced to explain the influencing factors. The other is the three-dimensional phase diagrams of annealed semiconductor-metallic films systems. From this diagram all the phase transitions can be found.     

Dynamic temperature crystallization behaviour of amorphous and liquid Mg70Zn30 alloy

The crystallization behaviour of the amorphous and liquid Mg₇₀Zn₃₀ alloy was investigated using a dynamic temperature X-ray diffraction method (DTXD). The sequence of phases crystallizing from the amorphous state with increasing temperature was found to be the same as that of the phases crystallizing from the liquid state with decreasing temperature. At low heating rates (i.e. 20K/h), it was found that the alloy Mg₇₀Zn₃₀ underwent a crystalline-amorphous transformation in the solid state, first at 440 K then at 590 K. This alloy showed the phenomenon of multimorphy; the different crystal structures form due to a macroscopic structural quantization effect. Structural data of new phases, discovered during this work, are given.     

Small-angle X-ray scattering study on the structure and crystallization of amorphous Fe-P-C alloy

The change in structure of an amorphous Fe-P-C alloy during ageing was examined using small-angle X-ray scattering (SAXS) measurement and transmission electron microscopy. The SAXS intensity was related to two different types of scattering regions depending on ageing time and temperature. The major scattering was from the crystalline particles, which had two-phase lamella structures. The average thickness of the lamellae remained constant at about 5 nm during ageing. The interlamella distance was three to five times the lamellar thickness in the regular packing region. Another minor scattering was interpreted as being caused by the local ordering of atomic configuration in the amorphous state. The average size of the scattering region was 1.8 to 2.4 nm and quite similar to the critical range proposed by Giessen and Wagner, beyond which the shortrange order disappears.     

Magnetic properties and surface crystallization induced by selective oxidation in Fe-B-Si amorphous alloy

The relationship between the annealing atmosphere and the magnetic properties of Fe_78.5B₁₃Si_8.5 amorphous alloy has been studied, showing that annealing in nitrogen, argon, hydrogen and air significantly improved the iron loss of the amorphous ribbon, giving much better results than annealing in an H₂ + H₂O atmosphere. A boron-depletion zone with the alloy composition O to 3 mol % B and 9 to 11 mol% Si was detected by Auger electron spectroscopy under the oxide film formed during annealing in H₂ + H₂O. The iron crystalline phase is formed only on the ribbon surface after annealing in H₂ + H₂O. A mechanism is proposed explaining the deleterious effect of annealing in the H₂ + H₂O, whereby the H₂O in this atmosphere selectively oxides boron in the amorphous alloy to form a B₂O₃ film and the boron-depletion zone, and the alloy in this zone is then crystallized into -Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous alloy ribbon (which was observed by transmission Mössbauer spectroscopy) and thus deterioration of the iron loss.     

The activation energies of the crystallization of amorphous Ni81 P19 alloy films

In situ transmission electron microscopic observations were carried out to study the crystal growth kinetics of amorphous Ni₈₁ P₁₉ alloy films prepared by vacuum deposition. In the first stage of crystal growth a metastable Ni₃P phase with hexagonal symmetry appeared. The growth rates were independent of time at a given annealing temperature. The activation energies along [1 0 0] and [1 1 0] directions were estimated to be 3.12 eV for the 55 nm thick and 3.22 eV for 20 nm thick film samples. Similar measurements for the stable and the metastable phases of thin foil samples were also carried out. The smaller activation energies for the foil samples than the film samples are explained by assuming that the compositional requirement at the crystalline-amorphous interface and the jumping of atoms to the crystal sites occur in series.     

The crystallization of the amorphous alloy Fe40Ni40P14B6

The isothermal transformation behaviour of the metallic glass Fe₄₀Ni₄₀P₁₄B₆ between 320 and 400° C is described. Crystallization occurs by a eutectic mechanism to form Fe-Ni austenite and a body-centred tetragonal phase which is isomorphous with Fe₃P and Ni₃P. The eutectic crystals have a barrel shape such that the c-axis of the tetragonal phase is parallel to the barrel axis. The orientation relationship between the two phases is 1 1 0T 1 1 0 and 0 0 1T 1 1 2. The austenite phase contains (1 1 1) twins.     

Surface crystallization of amorphous Fe-B-Si alloy annealed in a gas atmosphere containing organic vapour

The relationship between the annealing atmosphere and the magnetic properties of Fe_78.5B₁₃Si_8.5 amorphous alloy has been studied, showing that annealing in an inert gas atmosphere containing a borosiloxane resin significantly improves the core loss of the amorphous ribbon, and that annealing in an inert gas without any organic resins, gives much better results than annealing in an inert gas atmosphere containing cellulose and vinyl acetate resins. A boron-depletion zone was detected by Auger electron spectroscopy under the oxide film formed during annealing in the inert gas atmosphere containing cellulose and vinyl acetate resins. Annealing of the amorphous ribbon in the cellulose and vinyl acetate resins selectively oxidizes boron in the alloy to form a B₂O₃ film and a boron depletion zone; the alloy in this zone is then crystallized into -Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous ribbon and thus deterioration of the core loss. On the other hand, annealing in the borosiloxane resin results in neither selective oxidation of boron nor surface crystallization of the amorphous ribbon