Low-doped LM2 molybdenum alloy is obtained by the multiple electron-beam melting of Mo with the addition of 0.02 wt

The influence of heat treatment and deformation on a change in the structure of amorphous alloys Co67Fe7Si12B9Nb5, Al87Ni8Y5, Al88Ni6Y6, Al87Ni8Gd5, Al87Ni8La5, and Zr50Cu15Ti16Ni19 obtained by melt quenching is studied. It is established that both heat treatment and deformation lead to the formation of a heterogeneous structure, while structure inhomogeneities can be due to the formation of regions both with different concentrations of components (during heat treatment) and/or with a different density (free volume concentration). At the early stages of crystallization, the phase composition of the emerging structure depends on the type of impact on the amorphous structure and processing parameters (temperature, and type and degree of deformation). The sizes of nanocrystals and the fraction of the nanocrystalline component depend on the history of the sample.

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 structure of the side surfaces of the bulk Zr62Cu22Fe6Al10 amorphous alloy before and after compressive deformation at room temperature was studied using X-ray diffraction and scanning electron microscopy (SEM) methods. After preparation, the samples of the amorphous alloy had a square cross section of 5 × 5 mm and a length of 40 mm. Examining the side surfaces of the samples allows one to avoid influencing the surface structure of a tool used for deformation. The plastic deformation of amorphous alloys occurs through the formation and propagation of shear bands. During compressive deformation at room temperature, a system of steps was formed on the end surfaces of the sample caused by shear bands coming to the surface. Steps on surfaces have different sizes (thickness and height). It was established that the structure of large steps is complex: they consist of elementary steps 15–30 nm thick. The local deformation was estimated based on the size of the steps. The formation of a small number of nanocrystals during deformation was discovered. The nanocrystals are approximately 10 nm in size. The results obtained open a new direction for research into the structure of deformed amorphous alloys and nanocrystallization processes under the influence of deformation.

The shear bands formed under rolling in an amorphous alloy and their relation with the steps on the surface have been investigated. The studies were carried out by scanning, transmission electron, and atomic force microscopy. It was shown that a shear band began on a surface step. The thickness of the shear band was about 10 nm and varied from place to place. Secondary shear bands were found, which were located at an angle of 70 degrees to the shear band come out to the surface. The regions of the shear band had light and dark contrast, which indicated a change in the density of an amorphous phase along the shear band. The steps on the surface had a complex shape and consisted of elementary steps. The thickness of the elementary steps corresponded to that of the shear band.

— The effect of excess free volume on the structure and crystallization of amorphous metal alloys is considered. Its change is an important characteristic of such alloys. The changes in the free volume during structural relaxation, aging, heat treatment, deformation, and irradiation are given. It is shown that the fraction of excess free volume in the material depends on the composition of the alloy and the conditions for its preparation and changes under various external influences, which can contribute to both a decrease and an increase in the fraction. An increased fraction of excess free volume affects the physical properties and evolution of the structure and contributes to the acceleration of crystallization of the amorphous phase. The ability to control the fraction of free volume in a sample opens up new ways to control the structure and, as a result, the properties of materials.

Changes in the structure of amorphous alloys under deformation by high-pressure torsion, multiple-pass rolling, and pressure treatment have been studied using X-ray diffraction and scanning electron microscopy. It has been shown that under all types of deformation, shear bands are formed in amorphous alloys, which are regions of lower density compared to a surrounding undeformed amorphous matrix. Shear bands are regions of an increased free volume; the formation of bands results in steps occurring on the surface of samples. The number of shear bands and the surface morphology of deformed amorphous alloys are determined by the deformation type and physical properties of a material.

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.

Amorphous microwires of Fe 73.8 Si 13 B 9.1 Cu 1 Nb 3.1 andFe 77.5 Si 13.5 B 9 composition fabricated by the Ulitovsky--Taylor method were studied. The samples with the glass shell removed were heated at temperatures of 753 K and 703 K for 20 min, afterwards, their structure was examined using X-ray diffraction. Subsequently, the thermally treated samples were chemically etched and X-ray diffraction study of the structure was again carried out. Experimental results on the predominant crystallization of near-surface regions were discussed assuming that mechanical stresses affect the nucleation and growth of nanocrystals. Keywords: amorphous materials, stress distribution, nanocrystallization, X-ray diffraction.

Amorphous microwires of Fe73.8Si13B9.1Cu1Nb3.1 and Fe77.5Si13.5B9 composition fabricated by the Ulitovsky–Taylor method were studied. The samples with the glass shell removed were heated at temperatures of 753 K and 703 K for 20 minutes, afterwards, their structure was examined using X-ray diffraction. Subsequently, the thermally treated samples were chemically etched and X-ray diffraction study of the structure was again carried out. Experimental results on the predominant crystallization of near-surface regions were discussed assuming that mechanical stresses affect the nucleation and growth of nanocrystals.

The bulk-inhomogeneous crystallization of amorphous microwires of the composition Fe73.8Cu1Nb3.1B9.1Si13 is studied. An assumption is put forward concerning the influence of the inhomogeneous distribution of tensile and compressive stresses in the bulk of microwires on their crystallization. It is established that, at the initial stages of crystallization, crystallization occurs in the surface region of the microwire with a thickness of about 2.5 μm. It is established that the sizes of the nanocrystals in the surface region of the microwire are about 10 nm. It is found that the formation of an amorphous nanocrystalline layer on the microwire surface leads to an increase in the Mr/Ms ratio (ratio of remanent magnetization to saturation magnetization), which is associated with a decrease in the magnetic anisotropy due to a decrease in the stress level during heat treatment and nanocrystallization. The chemical etching of annealed microwires leads to a significant increase in the Mr/Ms ratio, which is due to an increase in the relative volume of the central domain layer. The results obtained indicate the potential for creating composite amorphous-nanocrystalline structures based on microwires. In the case of microwires of Fe73.8Cu1Nb3.1B9.1Si13 composition, the predominant crystallization of the surface layer can increase the effect of the giant magnetic impedance. Such objects may have potential applications in sensorics, in particular, in magnetic field and strain sensors.

The parameters of shear bands and their relationship with the nanocrystallization process in the Al87Ni8La5 amorphous alloy under deformation were studied by X-ray diffraction, high resolution electron microscopy, and atomic force microscopy. Deformation of the samples was carried out by room temperature rolling and high pressure torsion methods. An increase in the deformation level was found to lead to an increase in the surface roughness, an increase in the step height, and the formation of Al nanocrystals. The thickness of the shear band, determined from the width of the minimum steps, does not depend on deformation type and is approximately 15 nm; the height of the minimum steps ranges from a few tenths of nm to 1.5 nm. The formation of nanocrystals occurs when the shear band power corresponding to the true deformation e = 4.42 is reached.

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.

This review describes the current state of research on the formation of a nanocrystalline structure in amorphous alloys under thermal and deformation effects. The processes of formation of nanocrystals in homogeneous and heterogeneous amorphous structures (nanoglass) are considered. Changes in the magnetic and mechanical properties during the formation of a composite amorphous-nanocrystalline structure with different structural parameters are analyzed. The possibility of amorphous phase rejuvenation from a partially crystalline structure under cryogenic thermocycling treatment is shown.

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 effect of the structure of alloying elements and their solubility in the main component of the alloy on the formation of nanocrystals in the amorphous phase is investigated. The mechanism of the formation of nanocrystals based on the similarity of short-range order in ordered regions of a heterogeneous amorphous structure and the structure of the crystallizing phase is considered. It is shown that the presence of structurally related ordered regions provides a large number of potential nucleation sites for nanocrystals and facilitates the process of nanocrystallization. Since the fraction of the crystalline phase formed by the primary crystallization reaction is determined by the phase-equilibrium diagram, an increase in the number of such regions leads to the formation of a structure with a smaller nanocrystal size. The parameters of the resulting nanostructure depend on the type of alloying element, its concentration, and also the solubility in the main metal component of the alloy. The results obtained indicate possible implementation of the mechanism of the formation of nanocrystals in ordered regions in the heterogeneous amorphous phase of metallic glasses.

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.

The surface morphology of amorphous alloys Co65Si12B9Ni10Nb4, Co67Si12B9Fe7Nb5, Co79Si12B9, Co67Fe5B20Nb8, Co67Si13B9Fe1Mn4, and Co56Fe16B20Ti8 exposed to a pressure of 5 GPa is studied by scanning electron microscopy. Under the action of applied pressure, steps appear on the surface as a result of the emergence of shear bands on the surface of the samples. The height of the steps is determined. To determine the geometric characteristics of the steps, the results of measurements of the steps in the images obtained at different angles of electron-beam incidence on the samples are used. The sample is mounted onto a special holder that makes it possible to tilt the sample. The experiments are carried out with sample plane positions perpendicular to the incident electron beam and at an angle of 45° with respect to the latter. The step heights in the samples vary in the range from 20 to 400 nm. The steps form systems that are arranged at an angle to each other. The bands are unevenly distributed over the sample surfaces. The structure of deformed samples is studied using the X-ray diffraction method. It is found that the alloys with a large step height have a partially crystallized structure with the formation of nanocrystals, while the alloys with a small step height remain amorphous.