A metastable phase forming during crystallization of an amorphous Ni70Mo10P20 alloy

The evolution of the structure of an amorphous Ni₇₀Mo₁₀P₂₀ alloy during annealing in the temperature range from 673 to 873 K is studied using x-ray diffraction and transmission electron microscopy. It is found that a previously unknown metastable phase forms during crystallization of the amorphous Ni₇₀Mo₁₀P₂₀ alloy. The morphology of the newly formed crystals is studied, the space group and the lattice constant are determined, and the atom positions for the phase that forms are proposed. It is found that the metastable phase is a phosphide whose composition is close to (Ni(Mo))₃P. We established that, as the temperature or the duration of annealing is increased further, the metastable phase turns into the equilibrium Ni₃P phase. The orientation relations between the metastable and equilibrium phases are determined.     

Mechanism of crystallization of the Ni70Mo10B20 alloy above the glass transition temperature

The phase transformations occurring in the Ni₇₀Mo₁₀B₂₀ alloy in the course of heating above the glass transition temperature are investigated using x-ray diffraction, transmission electron microscopy, high-resolution electron microscopy, and differential scanning calorimetry. It is shown that annealing of the alloy above the glass transition temperature leads to segregation of the amorphous phase into regions enriched with and depleted in molybdenum and/or boron. An increase in the temperature or time of annealing is accompanied by primary crystallization in regions of each type. Crystallization of the regions enriched with molybdenum results in the formation of face-centered cubic crystals of a molybdenum solid solution in nickel (phase 2). Nickel boride crystallizes in the regions enriched with boron. The face-centered cubic phase (phase 1), which is similar to pure nickel, crystallizes in the regions depleted in molybdenum and boron. Nanocrystals of phase 1 are free of defects. Nanocrystals of phase 2 with larger sizes contain a great number of defects.     

Phase segregation in the Fe90Zr10 amorphous alloy under heating

A study of the changes in the structure of melt-quenched Fe₉₀Zr₁₀ amorphous alloys by x-ray diffraction, Auger spectroscopy, and transmission electron microscopy is reported. The samples were subjected to isochronous (for 1 h) and isothermal anneals at 100–650 °C. It is shown that an amorphous alloy annealed for one hour at 300–500 °C crystallizes with formation of a supersaturated solid solution of Zr in α Fe and the intermetallic compound Fe₃Zr. Isothermal anneal at 100 °C for up to 7000 h produces nanocrystallites 110–30 nm in size, with fuzzy interfaces between the grains. An alloy subjected to such an anneal contains two solid solutions of Zr in Fe, having a cubic and a weakly tetragonal lattice. Crystallization taking place during low-temperature anneals is preceded by phase segregation of the alloy within the amorphous state. The lattice periods of the solid solutions have been determined. The possibility of the alloy crystallizing by spinodal decomposition during prolonged annealing is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1769–1772 (October 1998)     

PES study of amorphous alloy Fe40Ni40P20

The electron structure of amorphous Fe₄₀NI₄₀P₂₀ has been investigated before and after annealing by XPS and UPS (HeI, HeII). It is shown that the spectra of UPS were modified obviously by various degree of annealing. Composition and chemical states of the components on the surface of the sample are also presented and the effect of structural ordering on the density of states (DOS) of the valence band is discussed.     

Effects of nickel on the crystallization of Zr70Cu20Ni10 amorphous alloy

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are employed to investigate the effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy. We have found that the crystallization process of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is strongly influenced by the addition of nickel. Addition of 10 at% Ni to the Zr₇₀Cu₃₀ amorphous alloy makes the crystallization process proceed from a single-stage mode to a double-stage mode. The activation energy for crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is calculated to be about 388kJ·mol^-1 on the basis of the Kissinger equation. The effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy are discussed in terms of the genetics of metals.     

Investigation of radiation damage in amorphous Fe70Ni10P13C7

Technique of selective registration of Mössbauer spectra from recoil atoms formed in nuclear reactions /1/ was used for investigations of local damaged zones in amorphous Fe₇₀Ni₁₀P₁₃C₇ alloy irradiated by high-energy charged particles — 30 MeV protons and 50 MeV alpha-particles — up to doses of 10²² m^?2. From absorption spectra of the alloy before and after irradiation and emission spectra conclusions are made about a state of the alloy damaged zones nearby the stopped⁵⁷Co atoms formed in nuclear reactions. It is established that in the irradiated amorphous samples⁵⁷Co atoms are stabilized in γ-phase and iron carbides and phosphides, and crystallic phase of α-Fe is formed far enough from them. In the crystallic samples no amorphization or any other transitions take place.     

Study of the structural relaxation and crystallization in amorphous Fe80P20 alloy by mössbauer effect

The structural relaxation and crystallization of amorphous Fe₈₀P₂₀ alloys have been investigated by Mössbauer spectroscopy. The result indicates that the process of the crystallization of Fe₈₀P₂₀ makes slow progress and it was occur from outside into inside. The amorphous alloys may be classified into six different stages from amorphous to crystalline state during annealing.     

Self-propagating crystallization waves in the TiCu amorphous alloy

Self-propagating crystallization waves are detected and experimentally demonstrated in the Ti₅₀Cu₅₀ amorphous alloy obtained by the melt spinning (ultrafast quenching) method. High-speed thermographic recording has shown that crystallization waves can appear spontaneously at the heating of an amorphous strip to 300–350°С or at the local initiation by a hot tungsten coil of a small segment of the strip preliminarily heated to 230–250°С. In the former case, the crystallization wave propagates at a velocity of ~7 cm/s; in the latter case, the crystallization wave propagates in a self-oscillation mode at an average velocity of ~1.2 cm/s. The temperature gradient across the wavefront is about 150°С. The samples crystallized in the self-oscillation mode have a characteristic banded structure with a smaller grain in depression regions. The crystallization product in all samples is the TiCu tetragonal intermetallic phase.     

Nanocrystal formation in gas-atomized amorphous Al85Ni10La5 alloy

An Al₈₅Ni₁₀La₅ amorphous alloy, produced via gas atomization, was selected to study the mechanisms of nanocrystallization induced by thermal exposure. High resolution transmission electron microscopy results indicated the presence of quenched-in Al nuclei in the amorphous matrix of the atomized powder. However, a eutectic-like reaction, which involved the formation of the Al, Al₁₁La₃, and Al₃Ni phases, was recorded in the first crystallization event (263°C) during differential scanning calorimetry continuous heating. Isothermal annealing experiments conducted below 263°C revealed that the formation of single fcc-Al phase occurred at 235°C. At higher temperatures, growth of the Al crystals occurred with formation of intermetallic phases, leading to a eutectic-like transformation behaviour at 263°C. During the first crystallization stage, nanocrystals were developed in the size range of 5 ～ 30 nm. During the second crystallization event (283°C), a bimodal size distribution of nanocrystals was formed with the smaller size in the range of around 10 ～ 30 nm and the larger size around 100 nm. The influence of pre-existing quenched-in Al nuclei on the microstructural evolution in the amorphous Al₈₅Ni₁₀La₅ alloy is discussed and the effect of the microstructural evolution on the hardening behaviour is described in detail.     

压力对Zr46.75Ti8.25 Cu7.5Ni10Be27.5大块非晶合金玻璃转变和晶化动力学的影响

利用X射线衍射和差示扫描量热分析研究了高温高压下Zr46.75Ti8.25Cu7.5Ni10Be27.5大块非晶合金的玻璃转变和晶化行为,结果发现压力降低了该大块非晶合金中的自由体积、热焓和晶化激活能.     

Phase transition in Pd40Ni10Cu30P20 bulk metallic glass under HP & HT

The phase transitions in Pd40Ni10Cu30P20 bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffraction measurements with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the melt differed from the primary phase crystallized from the starting amorphous solid upon heating, suggesting there existed a distinct mechanism in two cases.     

Short-range order, atomic structure, and dynamics of the amorphous alloy Ni80Zr20

The method of molecular dynamics with pair-interaction potentials calculated in terms of pseudopotential theory is used to model the rapid quenching process and to study the atomic structure and lattice dynamics of the alloy Ni₈₀Zr₂₀ in the amorphous state. The total and partial atomic radial distribution functions and the densities of vibrational states are calculated, and the nearest-neighbor interatomic distances and coordination numbers are determined. Fiz. Tverd. Tela (St. Petersburg) 39, 961–963 (June 1997)     

Crystallization of the amorphous Fe45Ni35Si10B10 alloy due to pulse heating

The effect of rapid heating on the stability of amorphous Fe₄₅Ni₃₅Si₁₀B₁₀ is studied in detail by Mössbauer spectroscopy. Structural relaxation as well as formation of crystalline α-Fe and γ(FeNi) is observed, depending on the heating and cooling conditions applied.     

Structural segregation in amorphous Fe40Ni40P14B6 under heat treatment and natural ageing

Transmission and depth selective conversion electron Mössbauer spectroscopy (DCEMS) were applied usefully to study structural transformation in the bulk and in the surface layer in a≈50 and 100 nm thick amorphous alloy that was subjected to annealing and natural ageing. Analysis of the hyperfine field distributionsP(H) shows the segregation of the amorphous matrix.     

The activation energy of crystallization of amorphous Fe40Ni40P14B6

The isothermal crystallization of Fe₄₀Ni₄₀P₁₄B₆ (Metglas 2826) has been studied by transmission electron microscopy, using static observations of partially crystallized ribbons at room temperature and in situ dynamic registration of the crystallization process at elevated temperatures. At all temperatures crystallization takes place by the nucleation and growth of individual crystals. Analysis of the transformation kinetics allowed to determine the nucleation rates and the activation energy for crystal growth. The growth velocity of the crystal phase was found to be controlled by the diffusion coefficient of phosphorus in this alloy withD ₀=2.5×10^10±1cm{swu2}/s andQ=(3.4±0.15)eV.     

Clustering effect in the crystallization process of a CuZr amorphous alloy

The structural relaxation and crystallization processes of the Cu₅₀Zr₅₀ amorphous alloy have been studied by field ion microscopy (FIM) on an atomic scale. An interesting phenomenon which we call the clustering effect was observed for the first time as far as we know. In the temperature range 673–723 K, clusters consisting of 3, 4, or 5 atoms formed and migrated towards certain crystalline centers. They then combined with one another and rearranged to produce an ordered atomic array. This clustering process including the formation, migration, combination and rearrangement of clusters is considered as a structural relaxation process.     

Mechanisms of the enhancement of amorphous alloy crystallization under illumination

The effect of the enhanced crystallization of amorphous materials under illumination is discussed. The interaction of photons with atomic clusters, which initiates their transformation, is considered. The mechanisms of the enhancement of amorphous alloy crystallization under illumination are described and quantitatively characterized.