The crystallization process of an Al87Ni6Nd7 amorphous alloy has been studied. It has been established that the crystallization of an amorphous alloy occurs in three stages, and the temperatures and activation energies of each crystallization stage have been determined. At the first crystallization stage, Al nanocrystals are formed; at the second stage, in addition to Al nanocrystals, the crystals of an Al11Nd3 phase are precipitated from the remaining amorphous phase. At the third crystallization stage, a previously unknown crystalline phase is formed. The structure of the new phase has been determined.

The influence of plastic deformation on the formation of nanocrystals in the Al87Ni6Nd7 amorphous alloy was studied using X-ray diffraction analysis. It has been shown that the preliminary deformation of the amorphous alloy accelerates the crystallization of the amorphous phase and can lead to the formation of smaller nanocrystals compared to heat treatment. The size of nanocrystals and their number depend on the treatment conditions of the amorphous phase: when preliminary deformation is used, the size of nanocrystals formed during annealing is smaller than that in an undeformed sample and the proportion of nanocrystals is slightly higher. In samples subjected to preliminary deformation by rolling, a gradient structure is formed: the proportion of nanocrystals decreases with distance from the surface into the depth of the sample. The size of nanocrystals changes slightly with changing distance from the sample surface. The results show that preliminary plastic deformation can be an effective method to obtain a nanocrystalline structure with different proportion and sizes of nanocrystals in the amorphous phase. This is important for creating highly functional materials with outstanding physicochemical properties. The results obtained significantly expand the existing understanding of the mechanisms of formation of nanocrystals in the amorphous phase under external influences.

The effect of protective coatings on the crystallization of amorphous Co-based alloys was studied using the methods of X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The crystallization of the amorphous alloys was studied on as-prepared samples, deformed samples, and deformed samples with a protective coating. After heat treatment, the fraction of the crystalline phase in the pre-deformed samples was higher than in the undeformed samples. When using a protective coating, the fraction of nanocrystals formed during heat treatment increased. The size of the crystals formed in deformed samples was smaller, and in the deformed samples with a protective coating, they were slightly larger than in the corresponding initial samples. The reasons for the differences in the formed structure in the amorphous alloys under study are discussed in terms of free volume.

The effect of free volume on the crystallization of amorphous Fe78Si13B9 ribbons was studied using ultrasonic and thermal treatments. To maintain free volume under heating, amorphous samples were coated with a special protective Ta coating. It has been shown via X-ray diffraction that the fraction of the crystalline phase in the annealed coated amorphous ribbons is higher than in the corresponding uncoated samples. The use of ultrasonic treatment and the application of a protective coating lead to the formation of a larger proportion of the crystalline phase during annealing. Differences in crystallization kinetics are discussed under the assumption that the concentration of free volume in amorphous samples affects their crystallization, as well as the role of the Ta coating preventing the release of free volume to the surface during heat treatment.

The influence of the free volume on the crystallization processes of Fe 78 Si 13 B 9 and Al 87 Ni 8 Gd 5 amorphous alloys is studied by X-ray diffraction. To study the influence of the free volume, two methods of amorphous-alloy deformation are carried out: ultrasonic treatment and multiple rolling. After deformation, a protective coating is applied to the amorphous alloys. It is shown that the deposition of a protective coating with a higher vacancy-formation energy compared to that in the amorphous alloys under study is an effective way to maintain the free volume in the amorphous phase, since it is thermodynamically unfavorable for the free volume to migrate from the amorphous phase into the coating material. Experimental data indicate that the preliminary deformation of amorphous alloys leads to an increase in the amount of free volume. An increase in the amount of free volume and its maintenance by the protective coating contributes to the significant crystallization acceleration of Fe 78 Si 13 B 9 and Al 87 Ni 8 Gd 5 amorphous alloys. The results obtained expand existing ideas about the processes of the crystallization of amorphous alloys and indicate the possibility of developing materials with different structural characteristics and, consequently, with different physical–chemical properties.

The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X=Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Ti8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy. Keywords: amorphous phase, crystallization, nanocrystals, magnetic properties.

The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X = Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Nb8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy.

The effect of free volume on the process of crystallization of an Al87Ni8Gd5 amorphous alloy is investigated. The deformation of the amorphous alloys leads to the formation of shear bands, which contain an enhanced free volume concentration. To retain the free volume the amorphous alloy was coated with a layer of a refractory metal. The structure of the Al87Ni8Gd5 alloy with a protective Ta coating was studied by X-ray diffraction and transmission electron microscopy methods. The fraction of the nanocrystalline phase formed in the amorphous samples with a protective Ta coating under annealing was found to be larger than that in the uncoated samples. The size of Al nanocrystals formed in the coated and uncoated samples is the same. A higher rate of crystal nucleation in the deformed amorphous samples with a protective coating is caused by a higher diffusion coefficient due to an enhanced free volume concentration.

The crystallization of amorphous alloys of Co-Fe-B-(Ti, Nb) system was studied by differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. It was determined that the alloying of amorphous alloys of Co-Fe-B system with elements having a bcc lattice promotes the formation of a metastable phase with this lattice during crystallization. Nanocrystal size and the fraction of the phase with a bcc lattice depend on the concentration of alloying components. When the concentration of bcc components increases, nanocrystal size decreases. When Nb (an element with a bcc lattice) is replaced by Ti (an element with an hcp lattice), the fraction of the bcc phase decreases, and multiphase crystallization (simultaneous formation of several crystalline phases) occurs. In Co56Fe16B20Ti8 alloy, the first crystallization stage consists of two steps. During the seemingly simultaneous formation of several crystalline phases, first a small quantity of the bcc phase and then Co23B6 and fcc-Co crystals are formed sequentially. All the results obtained indicate heterogeneous nanocrystal formation with the nucleation on structurally related ordered regions (on ordered clusters which consist of alloy components with the structure related to the crystallizing phase).

The structure of Co-based amorphous alloys (Co-Fe-B-Si-M system, where M = Ni, Nb, or Mn) after initial stage of crystallization was studied. In Co67Fe5Nb8B20 alloy, the formation of a new metastable phase has been detected and its structure has been determined. The dependence of the type of the crystal lattice of nanocrystals being formed on the structure of an alloying component (Ni, Nb, or Mn) and their solubility in the main alloy component was discovered. The dependence observed agrees with the assumption of heterogeneous nanocrystal nucleation on ordered regions in the amorphous phase, which have the same short-range order as the crystalline phase being formed. (C) 2021 Elsevier B.V. All rights reserved.

By means of computer simulation, we examined the effect of dispersity of filler length on electrical conductivity of two-dimensional (2D) composites with rod-like fillers. A continuous approach was used. Highly conductive zero-width rod-like particles were deposited uniformly with given anisotropy onto a poorly conductive substrate. Length of particles varied according to the lognormal distribution. Our simulation evidenced that slightly disordered systems may have both high figure of merit, i.e., both high electrical conductivity and optical transmission simultaneously, and high electrical anisotropy.

We simulated a random walk of rectangular particles on a square lattice with periodic boundary conditions. Two kinds of particles were investigated, viz., so-called "blind" and "myopic" particles. We found that steady state patterns occurred only for some values of the ratio L-x/L-y, where L-x and L-y are the linear sizes of the system, and only for "needles", i.e., the particles of size 1 x k. Different patterns were observed for "blind" and "myopic" particles.

Yuri Yu. Tarasevich, ∗ Nikolai I. Lebovka, 3, † Irina V. Vodolazskaya, ‡ Andrei V. Eserkepov, § Valeria A. Goltseva, ¶ and Valentina V. Chirkova ∗∗ Laboratory of Mathematical Modeling, Astrakhan State University, Astrakhan, Russia, 414056 Department of Physical Chemistry of Disperse Minerals, F. D. Ovcharenko Institute of Biocolloidal Chemistry, NAS of Ukraine, Kiev, Ukraine, 03142 Department of Physics, Taras Shevchenko Kiev National University, Kiev, Ukraine, 01033 (Dated: April 4, 2018)

Pattern formation occurring in a two-dimensional system of rod-like particles has been simulated using a lattice approach. The rod-like particles were modelled as linear k-mers of two mutually perpendicular orientations (k(x)- and k(y)-mers) on a square lattice with periodic boundary conditions (torus). Two different models of random sequential adsorption were used to produce an initial homogeneous and isotropic distribution of k-mers with different packing fraction values. By means of the Monte Carlo technique, translational diffusion of the k-mers was simulated as a random walk, while rotational diffusion was ignored, so, the k(x) - and k(y)-mers were considered as individual species. The system tended towards a well-organised nonequilibrium steady state in the form of diagonal stripes for relatively long k-mers (k >= 6) and moderate packing fractions (in the interval p(down) < p < p(up), where both the critical packing fractions p(down) and p(up) were dependent on k).

The electrical conductivity of two-dimensional films filled with rodlike particles (rods) was simulated by the Monte Carlo method. The main attention has been paid to the investigation of the effect of the rod alignment on the electrical properties of the films. Both continuous and lattice approaches were used. Intersections of particles were forbidden. Our main findings are (i) both models demonstrate similar behaviors, (ii) at low concentration of rods, both approaches lead to the same dependencies of the electrical conductivity on the concentration of the rods, (iii) the alignment of the rods essentially affects the electrical conductivity, (iv) at some concentrations of partially aligned rods, the films may be conducting only in one direction, and (v) the films may simultaneously be both highly transparent and electrically anisotropic.