bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the mechanical properties of a composite material based on silicon nitride by the indentation method
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Lukyanov Oleksandr , Chugunova Svitlana , Melnyk Victor , Goncharova Iryna
Published: August 2024

The purpose of the research was to determine the mechanical characteristics of silicon nitride ceramics and establishing optimal cutting regime of tool material. The composition (Si3N4+5%Al2O3+30%TiN) used for the manufacture of cutting tools were investigated. This composite was obtained by hot pressing of technical β-modification silicon nitride with an initial grain size of 0.6-1 μ with the addition of Al2O3 oxide to activate sintering and titanium nitride TiN in order to reduce the brittleness of the composite [1]. It was determine the following mechanical properties: Vickers hardness (HV), Knoop hardness (HK), fracture toughness K1C and plasticity characteristic δН. For brittle material, the use of the Knoop indenter allows to obtain high-quality indentation without chipping and cracks, which increases the accuracy of hardness measurement. To characterize the material's resistance to brittle fracture, the K1C value is used, which was determined by the indentation method based on the length of cracks that appear near the corners of the Vickers hardness indenter, and the value of δH was calculated from hardness measurements. The researched composite at room temperature has the following characteristics: HV=17,5GPa, НK=16,8GPa, K1С=8,35MN/m3/2, δН=0,52. To relieve internal stresses that are formed in ceramics during sintering due to different values of CTE (coefficient of thermal expansion) for Si3N4 and TiN, the composite was annealed at a temperature of 1050°C. After annealing, the mechanical characteristics remained at a fairly high level: HV=16GPa, НK=14GPa, K1С=7,4MN/m3/2, but δН increased to 0.55. Chipping of the edges of the cutting tool wasn’t observed. The research was carried out on the influence of cutting conditions on the mechanical characteristics of the tool. For hardened steel tools, the optimal regimes of cutting with silicon nitride ceramics were determined: t=0.02 mm, and S=0.5 mm/pass.
Comparative study of the photocatalytic activity of anatase nanoparticles formed in metatitanic acid and titanium (IV) isopropoxide systems
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Lavrynenko Olena , Zahornyi Maksim , Tyschenko Nadiya , Ragulya Andrey , Pavlenko Lesia
Published: August 2024

Anatase particles are widely used to create photocatalytic materials due to their low cost, biosafety, and high efficiency. The synthesis method and the nature of the precursor compound are important factors affecting the nanomaterials' phase and chemical composition, structure, and properties. The purpose of the present work is to compare the photocatalytic activity of nanosized particles of titanium dioxide obtained in the titanium tetraisopropoxide (TTIP) and metatitanic acid (MTA) systems. According to XRD data, all the obtained samples correspond to anatase. The samples obtained in MTA systems are characterized by a lower degree of crystallinity and differ in the content of S impurity, which is ~0.035% in MTA (1) and ~0.83% in MTA (2), respectively. The CSR of MTA (1) particles is 8 nm, the crystal lattice parameters are a = 0.3765 nm, c = 0.9435 nm, the degree of tetragonality c/a = 2.506, V = 0.134 nm3. The CSR of MTA (2) particles is 11.5 nm, the parameters a = 0.3748 nm, c = 0.9407 nm, c/a = 2.51, V = 0.132 nm3. The CSR of TTIP particles is 9.1 nm, the parameters a = 0.3775 nm, c = 0.9479 nm, c/a = 2.51, V = 0.135 nm3. The values of the point of zero charge of the samples are as follows: MTA (1) = 6.37; MTA (2) = 5.02 and TTIP = 8.8. A comparison of the photocatalytic activity of the particles was carried out by UV-VL spectroscopy. According to the degree of discoloration of the day's solutions with the initial concentration of 20 mg/dm3 within 60 min, the efficiency series is determined. For Methyl Orange: TTIP 63.5% < MTA (1) 67.9% < MTA (2) 74.4 %. For Orange G: TTIP 28.0% < MTA (1) 95.5% < MTA (2) 99.75 %. For Methylene Blue: MTA (2) 59.0 < MTA (1) 70.2 < TTIP 91.0, and for Rhodamine B: MTA (1) 63.6 < TTIP 69.0%. The probable cause of this difference can be both the crystal structure of the samples, the presence of sulfur in their composition as active additive, and the surface charge of the anatase particles.
The effect of chromium and molybdenum carbides alloing on corrosion resistance of mesostructure WC-Nі composites in chloride environment
Authors:   Bakul Institute for Superhard Materials of NAS of Ukraine, Kiev, Matviichuk Oleksandr , Vynar Vasyl , Ivashkiv Vasyl , Ratska Nadiia , Vasyliv Сhrystyna
Published: August 2024

Composites of the WC-Ni system are characterized by high wear resistance and crack resistance and are used in the sliding friction pairs [1]. Friction pairs based on WC-Ni alloys work well in such not electrically conductive environments as petroleum products and ammonia, but are not corrosion resistant in electrolytes such as chloride-containing solutions. One solution of the problem is to increase the corrosion resistance of the Ni binder. The aim of the work was to study the electrochemical characteristics of the WC-20 wt% Ni mesostructural alloy with the addition of 1%Cr3C2 and 0.5%Mo2C in chloride-containing solutions. The characteristics of corrosion processes were studied in the potentiodynamic mode in solutions: 3% NaCl+0.5% CH3COOH (pH 3), 3%NaCl (pH 7) and 3% NaCl + 0.0004% NaOH (pH 10). It is shown that the modification of the mesostructural alloy WC-20% wt. Ni by Cr3C2 and Mo2C contributes to shifting the electrode potential to more positive values. Taking into account the pH of the environment, there is an improvement in the potential values for both materials with a shift in the environment pH from 3 to 10. It was established that the corrosion current density of the WC- Ni alloy in a neutral 3% NaCl solution is 1∙10-3 mA/cm2. In alloy with 1%Cr3C2 and 0.5%Mo2C, the current density decreases by almost an order of magnitude and is 5∙10-4 mA/cm2. A similar trend is observed in acidic and alkaline environments. In an acidic environment, the corrosion current density of basic alloy and modified by carbides is 5∙10-3 and 1∙10-3 mA/cm2, in an alkaline environment – 6∙10-4 and 2∙10-4 mA/cm2, respectively. In an environment with a pH3, nickel is oxidized and goes into solution, while in an environment with a pH10, its partial passivation occurs. Therefore, alloying WC-Ni mesocomposition with 1%Cr3C2 and 0.5%Mo2C increases its corrosion resistance in environments with different acidity. The maximum corrosion resistance is observed in an alkaline environment.
Research of corrosion durability of porous materials with protective coatings
Authors:   Lutsk National Technical University, Povstianoi Oleksandr , Imbirovych Nataliia
Published: August 2024

Problem statement and objective. The modern stage of the development of materials science is accompanied by the emergence of new ideas for the creation and improvement of the technology of obtaining porous materials on LH15 steel powder, which, above all, are aimed at achieving high operational characteristics and reducing their cost. To apply a corrosion-resistant protective coating on porous materials, you can use the method of plasma-electrolytic oxidation (PEO), which is one of the most modern and promising methods of obtaining protective layers on the surface of metals and alloys. The properties of the obtained coatings are determined by the composition of the electrolyte and the modes of the PEO process [1]. Methods. To oxidize porous materials, salt solutions (NaCl, NaClO 3 , NaI, NaNO 3 ), acid solutions (HCl, phosphoric, citric, tartaric, and adipic) are used. The most common and simple electrolytes based on KOH solution. Electrolytes based on KOH solution and liquid glass were chosen for research. The synthesis of OKP on a zirconium alloy in an electrolyte of 10 g/l of KOH and 15 g/l of liquid glass and a ratio of Ia/Ic = 20/20 ensured the formation of an already pink coating with a fairly high microhardness (16 GPa). Main results and Conclusions. Coatings synthesized by the method of plasma-electrolytic oxidation have low porosity. This is explained by the fact that the coating is synthesized at high temperatures, as a result of which the pores melt. Therefore, to increase the porosity, we performed the synthesis at lower temperatures [2]. The use of porous materials for for tribotechnical purpose made it possible due to their improved properties (high chemical resistance, required mechanical strength) to increase the service life of the porous material by 1.5-2.0 times. According to the developed technological regimes, anti-friction products with a significantly lower cost and a higher coefficient of material utilization compared to traditional materials were obtained from a composite based on LH15 steel powder.
Synthesis of boron nitride from BCNO
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Pokropyvnyi Oleksii , Oleinyk Galyna , Pylypchuk Olesya , Danylenko Anstoliy , Solonin Yuriy
Published: August 2024

Boron nitride is well known as material for sythesis analogous of carbon fullerenes, nanotubes, and fullerites [1], as well as new phases. Hexagonal boron nitride (h-BN) has a complex of high performance such as high values of chemical stability and thermal conductivity, good electrical insulation and and lubricating properties, good ability to absorb neutrons. Due to its properties, h-BN is a multifunctional material, it is used to produce cubic boron nitride (c-BN), as high-temperature lubricants and coatings, when creating ceramic composite materials and the like. The h-BN powder is produced by various methods, one of the most common being the reaction of boric acid and melamine [2]. It was shown [3], that the formation of h-BN from boric acid and melamine occurs in the following sequence: first, the BCNO phase (at 350 °C and above) is formed, and with the synthesis temperature up to 800 °C and above in the BCNO phase also found h-BN. The objective of this work was to study the structure formation of BN with BCNO. The synthesis was carried out in a tubular flow quartz reactor at a temperature of 1200 °C in a stream of nitrogen [4]. The obtained samples were examined by transmission electron microscopy and X-ray phase analysis. The powder is composed of flat nanostructured particles. Particle sizes are 1-1.5 microns, and the sizes of the nanoscale substructure elements contained in them are in the range of 20-50 nm. Moreover, the smallest (20-30 nm) substructure elements have a rounded shape, while the largest ones are mainly polyhedral cut. According to Х-ray phase analysis, the sample consists of a hexagonal graphite-like phase of boron nitride. Analysis of microelectron diffraction patterns (MEGs) obtained from the powder confirms this result. However, a comparison of the features of 002 and 100 diffraction reflections in the form of rings on the MEG suggests that the sample also contains rhombohedral boron nitride.
Deformation-induced polymorphic transformation of β-SiС
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Radchenko Oleksandr , Gogaev Kazbek , Grigoriev Oleg , Bega Mykola , Stepanenko Artur , Itsenko Anatoliy
Published: August 2024

At different temperatures and pressures, some chemical compounds have different types of crystal structures or modifications, the stability of which is determined by the minimum thermodynamic potential [1]. Deformation of the material puts it in a less stable state and can cause polymorphic transformation [2,3]. Silicon carbide has two main modifications - β-SiC (low-temperature - cubic) and α-SiC (high-temperature - hexagonal) [4]. The transition temperature is 2100°C. Transformation under pressure was not investigated. Tapes were rolled from β-SiC powder to the maximum density (rolls with a diameter of 40 mm from the rolling mill had zero exit gap). The maximum normal contact stress did not exceed 0,7 GPa, the temperature did not exceed 40°С. Presses with a diameter of 15 mm were obtained from the original powder and crushed rolling stock. The density of the pressings was 1.05 and 1.23 g/mm3, respectively. The diffraction curves of the samples were taken in discrete scanning mode on a DRON-ZM diffractometer in monochromatized Cu-Kα radiation. The ratio of the atomic radii of carbon and silicon does not allow obtaining simple dense spatial structures [5]. Quantitative analysis of the phase composition of the powders performed using the software package Powdercell 2.4 showed that the phase composition before rolling was ~ 95% β-SiС and ~ 5% α-SiС, while after rolling - ~ 95% α-SiС and ~ 5% β -SiС. The integral width of the α-SiС lines obtained after rolling is significantly greater than the similar characteristic (26 - 46%) in the α-SiС powder supplied by the same company (Qinhuangdao Eno High-Tech Material Development Co. LTD, Китай). Results of X-ray phase analysis of granules from powders | β-SiС and strips rolled at the maximum load showed that polymorphic transformation of β-SiС into α-SiС took place during rolling.
Analysing the influence of structure morphology on weld metal properties, searching for relationships through multifractal indices
Authors:   National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», Shtofel Olha ,   E.O. Paton Electric Welding Institute, Holovko Viktor , Korolenko Daniil
Published: August 2024

The orientation of the structure has a significant effect on mechanical properties. If the grains are oriented in the longitudinal direction, i.e., when deformed along the crystallographic planes, which characterise the direction of grain growth during crystallisation, the ductility, as well as the short-term and long-term strength of the alloy, increase. The orientation of the grains in the direction of maximum stresses eliminates the presence of transverse grain boundaries, so the development of cracks along the boundaries in the longitudinal grain orientation is more difficult than in the transverse or equilibrium structure. The paper shows a solution to the problem of finding the angle of inclination of crystallites, calculating their sizes on the example of a model; the connection with the fractal parameter and mechanical properties of the distribution by angles of misorientation of the real structure. The model contains several objects of an arbitrary elongated shape. The task is to determine the orientation of the grains by finding the angle of inclination of each object to the selected axis. The programme, written in phyton with the use of artificial intelligence, is designed to analyse objects of different geometries in the input image. The results of the work consist of two parts. The first part is the program code corresponding to the theory, and the second part is the analysis of the data obtained and comparison with the existing mechanical properties and fractal dimensions of the components. The programme includes: 1) Converting the image to a black-white scale. 2) Detecting various shapes in the image using a thresholding technique. 3) Calculating properties - the length, width, centroid, orientation and angle. 4) Create data files. Further processing of the data allows you to build distributions of orientation angles on a flat structure, analyse the mechanical characteristics and compare them with the fractal dimension of the images.
Microstructure of heat-resistant nikel alloy after high-temperature heat treatment
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Oksana Vlasova Oksana , Golovkova Mary
Published: August 2024

The aim of this work is to study the microstructure of heat-intensive aviation alloy Ni-Co-Al-Cr (GTE) before and after high temperature heat treatment (HTHT) in vacuum at temperature 1280 оС. The alloy GTE is a three-phase system consisting of a γ-solid solution based on nickel with an FCC crystal lattice, dispersion precipitates of the strengthening γ'-phase based on the intermetallic compound Ni3Al (not less than 60-62 vol.%) and monocarbides type MC based on alloying elements (Ta, Nb, W)C. During operation, the structure of the alloy is degraded with the formation of pores, cracks, a change in the crystallographic features of the gratings of the γ- and γ'- phases and their dimensional mismatch with the initial parameters. It was found that the alloy GTE has a dendritic-cellular microstructure with axes of dendrites of the first and second order between which there is an eutectic with precipitates of carbides of the composition (Ta, Nb, W)C, round and significantly elongated, and in the form of individual particles ranging in size from 1 to 25 μm and multiple pores 1-10 μm in size. After the HTHT, the γ'-phase cuboids typical of heat-resistant alloys GTE are formed, the ideality of the shape of which depends on the temperature and exposure at a given temperature. The hardening γ'-phase in the alloy after the HTHT has a different size and shape in the axes of the dendrite and in the interdendritic space. In the interdendritic space the particle size of the γ′-phase is approximately 1.5 to 2 times larger than the size of the γ′-phase in the dendrite body and is 0.2 - 0.8 μm. The thickness of the layer of γ-solid solution is 0.1-0.2 microns. Carbide precipitates of 1 μm and 5 μm in size are observed. In the area of carbide precipitates, the degeneracy of the structure and coagulation of particles of the γ′- phase are fixed. Thus, it was shown in the work that only by high-temperature heat treatment it is impossible to restore the microstructure of the heat-resistant nickel alloy GTE after operation.
Charge carrier defect-dopant complexes in ZrO₂ co-doped with yttria and scandia
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Vasiliev Oleksandr , Bekenev Valerii , Bilyi Vladyslav , Brodnikovskyi Yehor
Published: August 2024

Co-doping ZrO₂ with yttria and scandia is an attractive way to produce stabilized cubic zirconia with maximized conductivity and fine-tuned thermal stability for specific application conditions/temperatures. As co-doping may lead to formation of defects with similar dopant atoms (homogeneous) or with Y and Sc atoms (heterogeneous), which can impact ionic conductivity, the aim of this work was to clarify which configuration is a more probable case in the mixed system using DFT modeling. The dopant-vacancy complexes were modeled with oxygen vacancy residing closer to one of the dopant atoms (dipoles) and equidistant to two atoms[1] (tripoles) at 3.2 mol. % and as tripoles with vacancies arranged along the [111] direction in cubic zirconia at 10.3 mol. % of added oxide. The configurations were fully relaxed with Quantum Espresso software package with calculation parameters ensuring energy and atomic forces convergence within 1.0·10⁻⁸ eV and 2.7·10⁻² eV/Å respectively. The total energies of the relaxed configurations were used to analyze their relative stability. The dipole configurations showed instability with respect to tripoles for all cases, with homogeneous yttrium configurations having the smallest energy difference with the more stable tripoles of 3.9 meV/atom and the largest of 20.2 meV/atom for heterogeneous configuration with the vacancy near the yttrium atom; for the scandium case the difference was 13.1 meV/atom. Among the tripoles, heterogeneous case has better stability at low concentrations with mixing energy of -7.8 meV/atom, while homogeneous seem to be more stable at high concentrations (mixing energy is 4.2 meV/atom), suggesting a transition at some concentration threshold. As stabilization of cubic zirconia typically requires more than 8 mol. % of dopant, a simple linear dependence of ionic conductivity on the concentration of one of the dopants should be expected in practical co-doped systems.
Effect of TiC additive on elasticity and electrical resistivity of reaction sintered nanosized SiC matrix composites
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Vdovychenko Oleksandr , Gadzyra Mykola , Kolesnykov Anatoliy , Tkachuk Neonila , Ihor Hnylytsia Ihor Hnylytsia
Published: August 2024

Silicon carbide (SiC) is one of the most important engineering ceramic because of its good thermal conductivity, oxidation and corrosion resistance, and mechanical properties. The need in reliable electronic devices for operation under shock cyclic loads and shear stresses requires the study of a combination of electrical and mechanical properties of SiC-based ceramics. In contrast to high-cost hot sintering, pressureless sintering and liquid-state sintering are used to obtain relatively low cost SiC-based products of complicated shape with excellent mechanical properties. [1] SiC-matrix composite obtained by reaction sintering of nanosized silicon carbide powders with various amounts of nanosized titanium carbide (from 1 to 8 wt% in increments of 1%) introduced into the composition of the initial charge were studied. The process of infiltration of porous blanks was also carried out in an induction furnace at a temperature of 2273K. Elastic characteristics were calculated based on the results of determining the density of samples using Archimedes method and the velocities of longitudinal and transverse acoustic waves using the pulse-echo and resonant techniques. It was established that with an increase in the content of titanium carbide, the specific electrical resistivity of the composites SiC-TiC decreases from 49.4x10-5 Ohm*m to 5.8x10-5 Ohm*m, instead, the elastic characteristics change non-monotonically. Young modulus E and shear modulus G tend to increase in the range of 1 to 4% TiC, followed by a decrease. The values of the Young modulus E vary in the range of 256 to 348 GPa, and the shear modulus G - in the range of 104 GPa to 151 GPa. Instead, the values of Poisson ratio change with the opposite trend in the range from 0.15 to 0.28 and have a minimum for the material SiC-5% TiC. Possible reasons for the specified changes in electrical resistivity and elastic characteristics are discussed.
Modern technologies of synthesis, 3D printing and consolidation for the manufacture of products from composite materials based on refractory compounds
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Zgalat-Lozynskyi Ostap
Published: August 2024

The results of the conducted research became the basis for the development of technology for the synthesis and consolidation of composite materials based on refractory compounds for the manufacture of products that are operated in conditions of extreme temperatures, loads and aggressive environments, as well as the latest materials for 3D printing using Robocasting and FDM technologies. Scientific and practical approaches to obtaining wear-resistant composite materials based on refractory compounds are proposed. The novel approaches of consolidation consist in the use of non-linear modes of materials densification under electrosintering conditions, which made it possible to obtain a number of new composite nanomaterials (grain size ~ 50 nm). The composites based on silicon, titanium, zirconium and niobium nitrides demonstrate a level of wear resistance 2-3 times higher than existing industrial analogues [1] . The technology for the synthesis of composite nanodisperse powders based on silicon nitride in a single technological cycle and nonlinear modes of their consolidation by the methods of spark-plasma sintering and sintering with controlled compaction speed to obtain wear-resistant ceramic products with the effect of self-healing of defects has been developed. A batch of ceramic balls with a diameter of 12 mm and 14 mm was produced for a hybrid rolling bearing with an extended service life, which is promising for use in aviation technology. For the first time in Ukraine, the technology of 3D printing by the Robocasting method was introduced for the manufacture of products of complex shape from composite materials based on refractory compounds and biocomposites [2,3] . IIt has been proven that the use of spark-plasma and microwave sintering is promising for obtaining products of complex shape from polymer-ceramic blanks made by 3D printing by the layer deposition method [4].
Theoretical evaluation of mechanical properties of inverse opal structure
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Korobko Pavlo , Kuzmov Andrii
Published: August 2024

The study focuses on the theoretical evaluation of the mechanical properties of porous materials with an inverse opal structure which serves as the object of the study. The subject of the study is the process of transition from elastic to irreversible deformation. The purpose of this study is to apply the finite element method to model this process to reveal the relationship between the structural characteristics of materials, such as porosity and coating thickness, and their mechanical properties [1]. The yield surface was constructed by computational modelling on a representative cell with a number of points in the (p,τ) plane for several cases of inverse opal structure - for a highly porous uncoated structure and structures with an additional layer [2]. As a result of the study, yield surfaces of the structure under investigation were constructed for several porosity values, from 0.56 to 0.9. In the result of the work, the approximation of the numerical appearance of the yield surface by a Deshpande-Fleck crushable foam model available in finite element modelling packages was made [3]. The conclusions of the study show that the effective plastic properties of materials with an inverse opal structure significantly depend on their porosity level and the presence of additional coatings. The obtained yield curve for a porosity of 0.9 is close to the associated plastic flow law, which allows us to assess the material's behaviour under loading based on the results of the uniaxial stress state. However, for a structure with medium porosity and an additional coating layer, the surface becomes significantly unassociated, with a discrepancy of almost 30%. The application of the Deshpande-Fleck model for crushable foam in the approximation of the obtained numerical data from the study demonstrated the relevance of the model in describing the plastic behaviour of this structure only at high porosity values.
The impact of low-temperature heat treatment on the structural and magnetic properties of Pt-(Au-)-Co heterostructures
Authors:   Igor Sikorsky Kyiv Polytechnic Institute, Ukraine, Pedan Roman , Makushko Pavlo , Yavorskyi Yurii , Dubikovskyi Oleksandr , Bodnaruk Andrii , Burmak Andrii , Makarov Denys , Vladymyrskyi Igor
Published: August 2024

Utilizing thermally induced diffusion-driven structural phase transformations in multilayer stacks to facilitate the formation of functional thin films holds significant promise for applications in nanoelectronics and magnetic data storage [1]. Ferromagnetic thin films derived from Co-Pt alloys serve as a foundational material science platform for the advancement of diverse applications, including spin valves, spin orbit torque devices, and high-density data storage media. In the present study Co(10 nm)/Pt(10 nm)/substrate, Pt(10 nm)/Co(10 nm)/substrate, Co(10 nm)/Au(2 nm)/Pt(10 nm)/substrate, and Pt(10 nm)/Au(2 nm)/Co(10 nm)/substrate stacks were obtained by magnetron sputtering onto SiO2/Si(001) substrate. The as-deposited stacks were annealed in a vacuum at temperatures of 150 °C – 550 °C for 30 minutes. Structural and magnetic properties were studied by secondary ion mass spectrometry (SIMS), X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and VSM magnetometry. Diffusion coefficients were estimated using the Hall–Morabito and Fisher–Whipple approaches. It is demonstrated that the layer stacking significantly impacts the diffusion rate at temperatures where the diffusion is dominated by grain boundaries. The heat treatment of thin-film stacks enhances coercivity, attributed to short-range chemical ordering effects. Introducing an additional Au intermediate layer increases the coercive field of annealed sstacks by modifying exchange coupling between magnetic grains at grain boundaries.
Modification of dislocation concentration in GaN:Si films by non-thermal microwave radiation treatment
Authors:   V. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Redko Roman ,   State University of Telecommunications, Milenin Grigorii , Safriuk-Romanenko Nadiia , Redko Svitlana
Published: August 2024

Both photoluminescence spectra and X-ray diffraction of GaN:Si were measured during long term (one month) after processing in microwave field (2.45 GHz, 10 s, p=7.5W/cm2). It was obtained non-monotonous changes of detected characteristics of studied samples. Due to small energy obtained in chosen field alternative resonant mechanism was proposed to explain observed features. Transformation of the defect subsystem (impurity-defect complexes destruction and/or detachment and displacement of dislocations) could be realized due to resonant phenomena related with coincidence between the electromagnetic wave frequency and proper frequencies of dislocation oscillations [1] and ion-plasma oscillations of impurity ions [2]. At the resonant frequency with small attenuation, the amplitude and, therefore, the oscillation energy increase sharply. As soon as the oscillation energy becomes higher than the binding energy of defects, the noted changes occur in the state of the latter. The observed features of long-term changes in the PL band intensities and dislocations concentration for the semiconductors under investigation after treatments in microwave field has been well described by the offered physical-statistical model of the behavior of defects, which is based on the idea that the corresponding physical processes can be described as random events. This physical-statistical approach allowed us to estimate the diffusion coefficients of defects in epitaxial films of semiconductor compounds. Obtained information will be value for understanding sensor system natural aging due to presence external microwave fields
Structure and physical-mechanical properties of cast heat-resistant FeNiCrCuAl high-entropy alloys
Authors:   Physico-Technological Institute of Metals and Alloys, N. A. S. of Ukraine, Sergiienko Ruslan , Serhiiko Roman , Shcheretskyi Volodymyr , Verkhovliuk Anatolii , Shcheretskyi Oleksandr , Byba Ievgen , Roik Oleksandr
Published: August 2024

The crystal lattice of high-entropy alloys (HEAs) undergoes significant deformation, that is why HEAs have high strength, significant wear resistance and corrosion resistance in environments with high chemical activity [1]. This work was aimed at creating new heat-resistant high-entropy alloys, based on inexpensive elements and prepared from common master-alloys, studying their phase composition and structure, as well as determining their physical-mechanical properties. FeNiCrCuAl alloys do not contain such an expensive element as cobalt (Co), which is usually present in similar metallic systems. FeNiCrCuAl high-entropy alloys were made from a mixture of pure metals (Cu, Ni, Al), low-carbon ferrochromium (FeCr70C1), stainless steel (GX10CrNiMn-18-9-1) and cast iron (content, wt.%: C = 2.60, Si =1.80, Mn = 1.30, Ni = 17.00, Cr = 2.30, Cu = 3.60, S = 0.05, P = 0.07). The investigated alloys were prepared by lost foam and sand mold casting methods. The phase composition of the as-cast FeNiCrCuAl alloys is represented by three phases: BCC-ordered solid solution of type B2, FCC solid solution and complex carbides (FeCr)₇C₃. Carbides were formed due to the presence of carbon in the charge materials such as cast iron (C = 2.6 wt. %) and stainless steel (C = 0.1 wt. %). A wide number of different meltings were performed therefore the chemical composition of the alloys fluctuated and the period of the BCC lattice parameter varied from 2.8859 Å to 2.8983 Å, and the FCC lattice parameter was from 3.6406 Å to 3.6666 Å. The microstructural analysis of the optical photographs revealed that the structure of the alloys was heterogeneous and consisted of granular and lamellar dendrites and interdendritic space. The HEAs of the FeNiCrCuAl system are characterized by relatively high hardness and samples suffered brittle failure during tensile tests due to the presence of carbides and BCC phase. The Brinell hardness and tensile strength in the as-cast alloys were in the range of 275 HB to 415 HB and from 300 MPa to 748 MPa, respectively.
Advancements in Sintering: Exploring Emerging Techniques and Future Perspectives
Authors:   School of Engineering and Material Science, Queen Mary University of London, Grasso Salvatore
Published: August 2024

Ultrafast High-temperature Sintering (UHS) allows consolidation of ceramics in just a few tens of seconds. The green body is placed within a heater energized by the Joule effect at temperatures up to 3000 °C. The accelerated UHS thermo-kinetics induces unique far from equilibrium features. UHS clearly opens up novel opportunities in ceramics consolidation as it combines together ultrarapid firing cycles and ultrahigh temperatures. The talk summarizes recent upgrades of the UHS experimental setup in order to consolidate large parts [1] while using less energy [2] and avoiding undesired carbon contamination [3]. A direct comparison with conventional sintering confirms the “favorable” impact of accelerated heating and colling rates in terms of i) dramatic (up to 95%) reduction in energy consumed during the sintering process [4] ii) straightforward processing of transparent ceramics without need for external pressure and/or reducing atmosphere (i.e., hydrogen) [5] iii) suppressed volatilization of light elements [6] iv) enhanced sinter-activity in high entropy oxides [7].
Prediction of nanopowder based tape surface roughness and density from a suspension rheological data
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Ivanchenko Serhii
Published: August 2024

To create a model for predicting the hydrocluster size in polymer-powder (PVB-BaTiO3) tape casting suspensions, a relation between the Peclet number and viscosity was studied. We used two suspensions with identical composition but different powder size (24 nm and 500 nm). Rheological studies of the dispersion with known-size particles make it possible to calculate the Peclet Number for this dispersion using equations [1], [2]: Pa=(6πr³ γη)/kT Where r – hydrocluster radius, γ – shear rate, η – viscosity, k – Boltzmann constant, T – temperature The relation between the Peclet number and viscosity fits a power low model Pe= (nanopowder) and Pe= (submicron powder) By applying this model to a flow curve of the tape casting suspension, where viscosity is known for each shear rate value, it is possible to calculate a hydrocluster diameter (d) using the equation: d=2∛(PekT/6πγη). Applying this model to rheological data of the nanopowder suspension showed a change in hydrocluster size from 208 to 60 nm, and for the submicron powder suspension, from 3520 to 924 nm. For a surface with the smallest possible roughness, assuming that the powder particles are spherical and tightly packed, the packing factor (φ) is 0,74. In this scenario Ra = d·(1/8), Rz = d·(1/2). In the case of non-dense packing of spheres (φ=0,68) Ra = d·(3/16), Rz = d·(3/4) [3]. The developed method was applied to compare roughness predictions based on calculated hydrocluster size with experimental data obtained from optical profilometry of the tape's surface. Predicted roughness for non-dense packing (φ=0,68) of the nanopowder tape is Ra=39 nm and Rz=156 nm. For the dense packing (φ=0,74) Ra=26 nm and Rz=104 nm. Experimental data: Ra=26 nm and Rz=100 nm. For the submicron powder tape Ra=265 nm and Rz=1062 nm (non-dense packing, φ=0,68) and Ra=177 nm, Rz=707 nm (dense packing, φ=0,74). Experimental data: Ra=261 nm and Rz=1076 nm. The error of predicted data is ranging from 1 to 4 %.
Electrochemical synthesis of ultra-dispersed tungsten powders in molten salts
Authors:   V.I. Vernadsky Institute of General and Inorganic Chemistry of the Ukrainian National Academy of Sciences, Kuleshov Serhii , Medvezhynska Olha , Novoselova Inessa , Omel’chuk Anatoliy , Bykov Valerii
Published: August 2024

The development of energy-efficient and environmentally friendly methods for producing ultrafine tungsten powders and its compounds is an urgent task due to the wide range of their applications. The method of electrochemical reduction of W in molten salts opens up new prospects for obtaining nano-sized tungsten powders and coatings of high purity from various precursors (oxides, sulfides, nitrides) of different morphologies and structures at low temperatures (600–900°C). The article presents the results of electrolysis of tungsten oxygen-containing compounds in molten mixtures of NaCl, KCl, CaCl2 , NaF. Both the traditional reduction of tungsten from precursors (Na2W2O7 , Na3WO3F3) dissolved in the electrolyte and the deoxidation of the solid WO3 and CaWO4 (Cambridge FFC process) were used. Tungsten powders were obtained by potentiostatic electrolysis (potentials range -1 – -3 V) at 750 °C using solid Pt or liquid Ga cathodes and different electrolyte compositions. Detailed information is presented in [1-3]. Depending on the synthesis conditions and the electrolytes composition, dispersed (30–50 nm) tungsten powders with a current yield of 45–70% were obtained. It was established that the current efficiency and final product characteristics are affected by both standard electrolysis conditions (temperature, cathode potential, current density, etc.) and other conditions: tungsten precursors (the morphology of W obtained from Na2W2O7 is characterized by a well-ordered dendritic shape and from CaWO4 by a fibrous structure with spherical inclusions); cathode material (the use of a liquid Ga cathode improves the processes efficiency) and the mechanism of chemical and electrochemical reactions. Thus, the electrochemical synthesis in molten salts can become an alternative to traditional methods of tungsten obtaining. The optimization of the conditions of these processes will make it possible to synthesize of W-Co alloys or powders (coatings) of binary and ternary carbides.
Electromagnetic properties of AlN-based composite materials with C and Mo additives
Authors:   Bakul Institute for Superhard Materials, NASU, Serbeniuk Tetiana , Prikhna Tetiana , Kalenyuk Oleksii , Futimsky Sergii , Sverdun Volodymyr , Shapovalov Andrii , Karpets Miroslav
Published: August 2024

The new composite materials with a high level of dielectric constant were created on the AlN-based. These materials were obtained by the hot pressing method at temperatures of 1800-1820 °C and a pressure of 15 MPa from powders mixtures AlN-Y₂O₃-5%C(soot), AlN-Y₂O₃-3%C(diamond powder - DP), AlN-Y₂O₃-5%C(DP)-5%Mo. The structural and phase composition of the composites was investigated by X-ray phase analysis using the Rietveld method and using a Zeiss Evoma15 SEM. The measurements of the complex dielectric constant in the frequency range of 12.4-18 GHz were carried out by the waveguide method using the Keysight P9375A vector microwave circuit analyzer. The main AlN phase and the presence of new phases: С(graphite), Al₃(O,N)₄, and Al in the materials structures were revealed by the X-ray phase method. The graphitization process of DP is characteristic for these compositions and at free sintering [1]. In addition, the formation of Mo₂C is observed in the system AlN-Y₂O₃-C(DP)-Mo. Also, thanks to X-ray studies and SEM with analysis of the quantitative elemental composition in the main phases by the EDS method, was established the presence of a low concentration of O in the AlN lattice and was revealed the location of conductive phases (C, Mo₂C) in the structure of materials. The results of measurements of electrodynamic characteristics showed that the developed new composite materials with graphite phase inclusions have constant dielectric characteristics in the entire frequency range and are at the level of ɛr = 12.38-33.03 and tgδ=0.06-0.51. Composites with soot had the highest values of dielectric constant (33) and losses (0.51). Preservation of high dielectric characteristics of composites, and at the same time increasing the level of dielectric permeability, is achieved due to the features of structure formation, in particular, arrangement of conductive phases grains (C, Mo₂C) in the structure of composites and minimization of contacts between them.
On the peritectic dissolution of tungsten in liquid Al
Authors:   National Technical University of Ukraine Igor Sikorsky Kyiv Polytechnic Institute, Soloviova Tetiana
Published: August 2024

When manufacturing heat-resistant metal alloys based on the Ti-Al-W system, technological difficulties arise, which are due to the large difference in the physical properties of the alloy components. The difference in melting temperature causes intense evaporation of the low-melting component (Al) at the temperature of W dissolution in liquid Al in a melting furnace. Thus, to prevent evaporation, ligatures should be made, which will then be introduced during the preparation of the structural alloy. Methods. Microscopic analysis of samples on a light microscope (Jenaphot 2000 by Carl Zeiss) and a scanning electron microscope (SEM 106I by Selmi) and X-ray phase analysis (Rigaku Ultima IV). Main results. It is shown that the atomic dissolution of W in liquid Al is preceded by Rebinder’s enrichment of intergranular boundaries of W with Al, forming an intermediate ε- or ζ- phase and subsequent rafting of the W crystal in the liquid phase. Similarly, dendritic crystals of ε- and other intermediate phases that formed during the interaction of W and liquid Al through a cascade of peritectic reactions are dissolved. Conclusions. 1.The direct dissolution of W in liquid Al at1300 °C is either absent or marginally small. 2.The reaction between liquid Al and W involves the intense diffusion of Al atoms along the grain boundaries and sub-boundaries. This results in the formation of layers of an intermetallic phase ε (T<1300 °C) or ζ (T>1300 °C). The formation of two interfaces of the intermetallic phase (ε/L and ε/W or ζ /L and ζ /W) leads to diffusion of Al atoms from liquid Al through the intermetallic phase to W. 3.The saturation of the ε-phase with Al at the ε/W interface and the ζ-phase at the ζ /W interface causes them to melt and fragment the W. This fragmentation increases the speed of peritectic melting of W, improves the macroscopic homogeneity of the ligature alloy, reduces high-temperature evaporation of Al, and reduces energy costs for the technological process.
Effect of heat treatment in hydrogen on the phase formation processes in nanoscale FePt and FePtPd films and their Raman spectra
Authors:   Educational and Research Institute of Materials Science and Welding National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Verbytska Tetiana , Horodnycha Daria , Shkarban Ruslan , Barabash Maksym , Makogon Iurii
Published: August 2024

Nanoscale films based on FePt(Pd) layers with an ordered L1o structure have a promising application both for ultra-high-density magnetic information carriers and for future spintronics devices. The purpose of these studies was to determine the effect of the heat treatment in the hydrogen environment and the Pd addition on the phase composition and structure of the films and their optical properties. Equiatomic Fe50Pt50 and Fe50(Pt0.75Pd0.25)50 films with a total thickness of 15 nm were obtained by magnetron sputtering on a SiO2/Si(001) substrate at room temperature. After deposition, the films were annealed in a hydrogen environment at temperatures of 400 - 700 °С for 1 h. The processes of the A1 into L1o phase transformation were investigated by X-ray diffraction, RHEED method and Raman scattering spectroscopy. The ordered L1o phase in both films begins to form at 400 °C. As the temperature rises, its amount increases. The Pd addition activates the ordering process and contributes to increasing the ordering degree, the formation of (001)-textured grains up to a temperature of 650 °C, but does not affect the size of the FePt or FePtPd coherent scattering regions. It was found that after annealing to 700 °C, only the L1o phase is observed in both films. The change in the Raman spectra confirms the presence of embodied hydrogen in the films and а two-phase state (A1+L1o) in the films up to a temperature of 650 °C, inclusive. The variation in Raman spectra and the luminescence effect are manifested in different structural combinations of FePt and FePtPd films. The non-linear change in the intensity of the Raman spectra is the basis for the appearance of forced Raman scattering effects. Enhancement of luminescence by the film allows to identify the structural A1into L1o phase transformation dynamics.
Substrate bias influence on the properties of ZnO:Al and ZnO:Al,N films deposited by magnetron sputtering
Authors:   Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Omeliana Pritsaka street, 03142 Kyiv, Ukraine, Karpyna Vitalii , Ievtushenko Arsenii , Olifan Olena , Mamykin Sergey , Kolomys Oleksandr , Strelchuk Viktor , Lytvyn Peter , Starik Sergii , Baturin Volodymyr , Karpenko Oleksandr
Published: August 2024

ZnO-based wide bandgap semiconductor oxides with a bandgap 3.3 eV have unique optical and electrical properties that make it promising for transparent electronics, optoelectronics and solar cells [1]. Magnetron sputtering (MS) attracts our attention due to the great possibilities for the deposition oxide films with good film adhesion, high deposition rates, film uniformity and stable composition of the deposited films. Traditionally the substrate potential at MS is grounded. The negative or positive potential applied to substrate (substrate bias) can influence the film growth as well. As to single-doped ZnO:Al and codoped ZnO:Al,N films the influence of substrate bias on their structure, and optical and electrical properties has not been studied yet in detail. In this work, we focus on the investigation of indicated properties of thin films deposited on Si and glass substrates by radio frequency magnetron sputtering in a layer-by-layer regime. Sample characterization was carried out by traditional instruments: X-ray diffraction, EDX spectroscopy, Raman scattering, photoluminescence, IR Fourier transform spectrometry, optical and electrical measurements. The experimental results will be presented and discussed. Shortly, the best crystalline quality demonstrates ZnO:Al films grown with the highest negative voltage bias of -30V. We have found that applying a negative bias voltage to the substrate during film growth allows us to increase the conductivity of ZnO:Al films three times compared to zero-biased ZnO:Al films deposited at the same conditions. ZnO:Al,N films show very high specific resistivity due to acceptor complex formation. It must be noted that all deposited ZnO:Al and ZnO:Al,N films demonstrate a high transparency of over 80 % with an optical band gap in the range 3.34-3.42 eV for ZnO:Al films while ZnO:Al,N films demonstrate band gap near 3.15 eV.