Structural-phase State Research Articles

Nonlinear Transport and Magnetic/Magneto-Optical Properties of Cox(MgF2)100-x Nanostructures

The aim of this work was to comprehensively study the effect of the variable atomic composition and structural-phase state of Cox(MgF2)100-x nanocomposites on their nonlinear transport and magnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on glass substrates were obtained by means of ion-beam sputtering of a composite target in the argon atmosphere in a wide range of compositions (x = 16–59 at.%). Using a low metal content in the nanocomposite, magnesium fluoride was kept in the nanocrystalline state. As the metal content increased, nanocrystalline cobalt was formed. The value of the resistive percolation threshold, xper = 37 at.%, determined from the concentration dependences of the electrical resistance of the nanocomposites coincided with the beginning of nucleation of the metallic nanocrystals in the MgF2 dielectric matrix. The absolute value of the maximum negative magnetoresistive effect in the nanocomposites was 5% in a magnetic field of 5.5 kG at a Co concentration of x = 27 at.%.

On the relationship between the properties of planar structures of non-ionic surfactants and their vesicular analogues – Niosomes

In recent years, the study of niosomes as nanocarriers alternative to liposomes has received increasing attention. In contrast to well-studied liposome membranes, many aspects of the behavior of analogous niosome bilayers have not been studied. This paper considers one of these aspects related to the communication between the physicochemical properties of planar and vesicular objects. We present the first results of comparative studies of Langmuir monolayers of binary and ternary (with cholesterol) mixtures of non-ionic surfactants based on sorbitan esters and niosomal structures assembled from the same materials. The Thin-Film Hydration (TFH) method in the gentle shaking version was used to produce the particles of large sizes, while small unilamellar high quality vesicles with a unimodal distribution of particles were prepared by TFH using ultrasonic treatment and extrusion. An analysis of the structural organization and phase state of monolayers based on compression isotherms and supplemented by thermodynamic calculations, as well as the results of determining the particle morphology, polarity and microviscosity of niosome shells, made it possible to obtain fundamental data on the intermolecular interactions of the components and their packing in shells and to relate these data to the properties of niosomes. This relationship can be used to optimize the composition of niosome membranes and predict the behavior of these vesicular systems. It was shown that cholesterol excess creates regions of bilayers with increased rigidity (like “lipid rafts”), which hinders the process of folding film fragments into small niosomes.

Corrosion-resistant steels based on Fe – ~13 % Cr: Heat treatment, corrosion- and wear resistance. Review

Martensitic stainless steels with 13 % Cr are widely used in many industries due to their high level of mechanical properties and acceptable corrosion resistance. The paper consolidates information about the guaranteed level of properties and the heat treatment conditions necessary for its implementation. The properties after the treatment proposed by the researchers are compared with the known properties for industrial metal. Dependences of hardness of the hardened steels of 13Cr type with 0.20 – 0.5 % C on austenitization temperature and accompanying changes in the structure were analyzed, the temperatures providing maximum hardening and the temperatures at which the steel ceases to harden were identified. Influence of the austenitization duration, heating and cooling rates on the steels properties is described. The review considers mechanical properties and corrosion resistance after quenching, quenching and tempering in relation to the structural-phase states of steels. It is shown in detail how the type of secondary phases during tempering, their quantity and distribution affect the corrosion resistance of steels with 13 % Cr. It increases with an increase in the heating temperature during austenitization and decreases with an increase in tempering temperature due to precipitation of Cr23C6 carbides and depletion of the matrix in chromium to concentrations below 12 %. The tempering temperature of 500 – 550 °C is recognized as the worst: due to the intense precipitation of carbides, the steel is not passivated, the corrosion rate is maximal. For steels of 20Kh13 type, low tempering quenching (for a combination of high strength, good corrosion resistance and satisfactory ductility) or, more often, high tempering at ~(650 – 700) °C (good ductility, satisfactory corrosion resistance) is recommended. For steels of 40Kh13 type, a temperature of ~700 °C is not recommended due to the increased concentration of carbides and insufficient corrosion resistance. Examples are given of increasing the wear resistance of steels of 40Kh13 type due to surface treatments, from nitriding to laser and plasma surface hardening.

FEATURES OF THE STRUCTURE AND PROPERTIES OF POWDERS OF MECHANOSYNTHESIZED TIN BRONZES AND SINTERED MATERIALS BASED ON THEM

The results of studies of the structural-phase state of copper and tin mixture powders (12-20 wt.% Sn), formed during high-energy mechanical processing in a planetary ball mill, are presented. The effects of mechanochemical synthesis of composites during sintering and formation of the structure of sintered bronzes are considered. The relationship between the tin content and the formation of grain-boundary segregations and their influence on the properties of materials is shown. Thus, an increase in the concentration of tin contributes to the acceleration of grain-boundary interactions, a decrease in the rate of bulk diffusion, followed by the formation of supersaturated bulk and grain-boundary solid solutions. For the composition of the mixture with a tin content of 18-20 wt.% during mechanochemical synthesis, grain-boundary supersaturation with tin is achieved by more than 2 times, which contributes to dispersion strengthening of sintered materials based on them and provides microhardness within 2.1-3.0 GPa in a temperature range of 20-800 °С.

Structure phase state and physical properties of YbMn1-xFexO3 compositions

Structure phase state and physical properties of YbMn1-xFexO3 compositions

The Effect of Heat Treatment on the Structural-Phase State and Abrasive Wear Resistance of a Hard-Anodized Layer on Aluminum Alloy 1011

The aim of this study was to evaluate the effect of heat treatment on the phase composition, hardness, and abrasion wear resistance of hard-anodized layers (HAL) on 1011 aluminum alloy. X-ray diffraction analysis revealed the Al2O3·3H2O phase in the structure of HAL synthesized for 1 h. While in the heat-treated HAL, aluminum oxide phases of the α-Al2O3(amorphous) and γ-Al2O3(amorphous) types were found. Treatment at 400 °C for 1 h increased the HAL microhardness from 400 to 650 HV, and its abrasive wear resistance with fixed abrasive by up to 2.6 times. The ranking of various ways of hardening aluminum alloys relative to the D16 alloy showed that the abrasive wear resistance of heat-treated HAL is 20 times higher. Plasma electrolyte oxidation increased the abrasive wear resistance of the D16 alloy by 70–90 times, and its coating with high-speed oxygen fuel by 75–85 times. However, both methods are complex, energy-consuming, and require fine grinding of parts. Despite the lower wear resistance of HAL, their synthesis is cheaper and does not require the fine-tuning of parts. Moreover, despite the low hardness of HAL at present, hard anodizing is already commercially used to harden engine pistons, clamshell rotators, and pulleys.

Novel CdS/CeO2/g-C3N4 nanocomposite for efficient phenol photodegradation under visible light

Higher electron transfer efficiency is an important way to improve the activity of photocatalysts. A novel Z-scheme CdS/CeO2/g-C3N4 nanocomposite was successfully synthesized by a solvothermal method, and its photocatalytic activity was evaluated by the degradation of phenol. The phase structure, morphology, surface structure, and atomic valence state of the as-obtained photocatalyst were characterized by XRD, SEM, TEM, FT-IR, XPS, and UV–Vis absorption spectroscopy, respectively. The CdS/CeO2/g-C3N4 nanocomposite exhibited a remarkable photocatalytic activity and a rapid degradation ability for phenol with a degradation rate of 95 % in 180 min, which was considerably better than those of pure CeO2 and CdS/CeO2 under the same conditions, suggesting a synergistic effect in the nanocomposite. The enhancement of the photocatalysis ability of the nanocomposite is mainly attributed to the higher adsorption capacity of three-dimensional porous g-C3N4 and the three-dimensional space electric field formed by its complex with CdS and CeO2. The three-dimensional porous structure is not only conducive to the efficient adsorption of pollutants but also provides active sites for photocatalytic reactions. The three-dimensional space and the network interconnection structure are conducive to the directional migration of photogenerated charges and increase the carrier lifetime. In brief, this work provides a new route to the design and synthesis of CdS/CeO2/g-C3N4 for colorless organic pollutants photodegradation under visible light.

Dynamics Of Structural-Phase States of Nanocrystalline ZrO2(CaO) During Sintering in a Constant Magnetic Field

Dynamics Of Structural-Phase States of Nanocrystalline ZrO2(CaO) During Sintering in a Constant Magnetic Field

Structural-Phase State and Properties of SiC Ceramics Obtained by Ultrasound-Assisted Liquid-Phase Sintering with Eutectic Additives

Structural-Phase State and Properties of SiC Ceramics Obtained by Ultrasound-Assisted Liquid-Phase Sintering with Eutectic Additives

Structure-Phase State, Mechanical Properties, and Corrosion Behavior of Quasicrystalline AlCuFeSc Coating

Structure-Phase State, Mechanical Properties, and Corrosion Behavior of Quasicrystalline AlCuFeSc Coating

IMPROVING THE PROPERTIES OF NICKEL-BASED SUPERALLOYS OF DIRECTED CRYSTALLIZATION BY OPTIMIZING THE CHEMICAL COMPOSITION

Purpose. It consists in establishing the influence of the chemical composition on the type, chemical composition and morphology of the primary carbides of the nickel-based superalloy, which allows to increase the operational properties of the parts through the structure of the carbide component.
 Research methods. Process modeling was carried out using the CALPHAD method. The initial data were the chemical compositions of model alloys with different concentrations of carbide-forming elements. The result of the calculation was the chemical composition of the carbides released in the corresponding systems. The experimental values were processed by statistical methods to obtain correlation dependencies of the “parameter-property” type and establish mathematical equations of regression models that optimally describe these dependencies.
 Results. The regularities of the effect of metal chemical composition on the morphology of carbides of MC type have been established. It is shown that depending on chemical elements introduced in the system, the basis of carbides can change, which causes a change in their shape and an increase in the crack resistance of the material. It is shown that the obtained dependences are closely correlated with metallographic studies of alloys of this class.
 Scientific novelty. The dependences of the influence of the chemical composition variation of the multicomponent system Ni-Cr-Co-Al-W-Re-Ta-Mo-Nb-C on the chemical composition and morphology of carbides have been established. This makes it possible to change the basis of the carbides, their composition and morphology, thereby improving the mechanical properties of the material, especially fatigue and heat-resistant characteristics.
 Practical value. An effective solution for establishing the structural-phase state of nickel-based superalloys by optimizing their chemical composition is proposed, which made it possible to improve the operational properties of the material. The established dependencies can be used in the optimization of the composition of industrial cast nickel-based superalloys and in the development of new compositions.

Two-step single-reactor synthesis of oleic acid- or undecylenic acid-stabilized magnetic nanoparticles by thermal decomposition.

Different iron oxides (i.e., magnetite, maghemite, goethite, wüstite), particularly nanosized particles, show distinct effects on living organisms. Thus, it is of primary importance for their biomedical applications that the morphology and phase-structural state of these materials are investigated. The aim of this work was to obtain magnetic nanoparticles in a single reactor using Fe(III) acetylacetonate as the initial precursor for the synthesis of Fe(III) oleate or Fe(III) undecylate followed by their thermolysis in situ. We proposed a new approach, according to which the essential magnetite precursor (a complex salt of higher acids - Fe(III) alkanoates) is obtained in a solvent with a high boiling point via displacement reaction of acetylacetone with a higher acid from Fe(III) acetylacetonate during its elimination from the reaction mixture under vacuum conditions. Magnetic nanoparticles (NPM) were characterized in terms of morphology, hydrodynamic diameter, and composition via several techniques, such as transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, Fourier-transform infrared spectroscopy/attenuated total reflectance, 57Fe Mössbauer spectroscopy, and X-ray diffraction. The effect of unsaturated oleic (OA) and undecylenic (UA) acids, which are both used as a reagent and as a nanoparticle stabilizer, as well as the influence of their ratio to Fe(III) acetylacetonate on the properties of particles were investigated. Stable dispersions of NPM were obtained in 1-octadecene within the OA or UA ratio from 3.3 mol to 1 mol of acetylacetonate and up to 5.5 mol/mol. Below the mentioned limit, NPM dispersions were colloidally unstable, and at higher ratios no NPM were formed which could be precipitated by an applied magnetic field. Monodisperse nanoparticles of iron oxides were synthesized with a diameter of 8-13 nm and 11-16 nm using OA and UA, respectively. The organic shell that enables the particle to be dispersed in organic media, in the case of oleic acid, covers their inorganic core only with a layer similar to the monomolecular layer, whereas the undecylenic acid forms a thicker layer, which is 65% of the particle mass. The result is a significantly different resistance to oxidation of the nanoparticle inorganic cores. The core of the particles synthesized using oleic acid is composed of more than 90% of maghemite. When undecylenic acid is used for the synthesis, the core is composed of 75% of magnetite.

Исследование теплофизических процессов получения различных алюмоматричных композитов

The possibilities of obtaining aluminum matrix composite materials of the composition Al−Al2O3 are considered by the method of liquid-phase oxidation of aluminum by purging the melt with oxygen. The obtained materials are a two-phase system with different concentrations of the solid phase. An algorithm for calculating the kinetics of aluminum oxidation in obtaining the oxide phase of an aluminum matrix composite is proposed. It is established that the beginning and completeness of the reaction on the surface of the gas bubble determines the synthesis of the oxide phase and is determined by the functions T(t), h(t) in the region of dynamic time delay, which, in turn, the queue is revealed as a function of the temperature in the contact zone of the gas bubble with the melt, taking into account the duration of the heating of the bubble along the cross section and the radius of the bubble itself. The microstructures of the obtained materials with different structural-phase state with variations in the time of purging and oxygen supply to the aluminum melt are presented

Gradient structural-phase states and properties of surface layer after nitro-oxidation

The phase equilibrium is considered, the formation of nitride phases during gas nitriding due to the presence of carbon in the iron steel matrix in all formed structural-phase states of the nitride layer, carbides are released, the dispersion and dispersion of which in the nitride layer depends on the nitrogen potential of the saturating atmosphere. During subsequent oxidation in water vapor, simultaneously with the formation of a surface oxide film during the exposure period, especially in water vapor with additives of complexion agents, during reaction-diffusion, gradient structural-phase states of low-nitrogen carbonitride, oxycarbonitride, and nitride phases are formed in the nitride layer. At the same time, the presence of oxygen in the furnace atmosphere positively affects the formation of the nitride layer and the internal nitriding zone. The corrosion resistance of gradient nitride-oxide diffusion coatings depends on the presence of a surface oxide layer consisting of magnetite and the ratio of modified nitrides and γ'-phase composition. At the same time, in the composition of the nitride layer, the composition of oxycarbonitrides with a larger proportion of the γ'-phase has the highest corrosion resistance with a lower rate of development of corrosion damage on the surface. The presence of a surface oxide layer in the structural-phase states of the nitride-oxide layer, providing a positive property gradient, can provide conditions for external friction during sliding friction.

Investigation of thermophysical processes of obtaining various aluminum matrix composites

The possibilities of obtaining aluminum matrix composite materials of the composition Al-Al2O3 are considered by the method of liquid-phase oxidation of aluminum by purging the melt with oxygen. The obtained materials are a two-phase system with different concentrations of the solid phase. An algorithm for calculating the kinetics of aluminum oxidation in obtaining the oxide phase of an aluminum matrix composite is proposed. It is established that the beginning and completeness of the reaction on the surface of the gas bubble determines the synthesis of the oxide phase and is determined by the functions T(t), h(t) in the region of dynamic time delay, which, in turn, the queue is revealed as a function of the temperature in the contact zone of the gas bubble with the melt, taking into account the duration of the heating of the bubble along the cross section and the radius of the bubble itself. The microstructures of the obtained materials with different structural-phase state with variations in the time of purging and oxygen supply to the aluminum melt are presented. Keywords: aluminum matrix composite material, high temperature oxidation, gas bubble.

Effect of filler Al-Mg-Mn wire and post-heat treatment on the structural-phase state and mechanical properties of laser welding of Al-Mg-Li alloy

In this work, complex studies of laser welding using filler aluminum wire of the Al-Mg-Mn system and post weld heat treatment were carried out in order to increase the level of mechanical properties of alloys of the Al-Mg-Li system. High-quality weld joints were obtained. The use of synchrotron radiation with a spatial resolution of 100 μm made it possible to scan the weld and the original alloy in detail. Subsequent heat treatment of the weld made it possible to form the strengthening phase δ'(Al3Li) and improve the mechanical properties. Energy conditions for obtaining a high-quality weld with wire: heat input ≈ 90.9 J/mm, energy per unit volume of the molten material ≈ 28.94 J/mm3.

Анализ механизмов упрочнения рельсовой стали при пластической деформации одноосным сжатием

Using the methods of scanning and transmission electron microscopy, an analysis was made of the evolution of the structure and defective substructure of rail steel under uniaxial compression up to a degree of 50%. It is revealed that the strain hardening has a multistage nature and is accompanied by a decrease in the scalar and excess dislocation density and fragmentation of pearlite grains, which increases with increasing strain. Fracture of cementite plates proceeding through the mechanisms of their dissolution and cutting by mobile dislocations is revealed. On the basis of data on the structural-phase states, the defective substructure of rail steel, obtained by the methods of modern physical materials science, a quantitative analysis of the mechanisms of hardening of rail steel at degrees of compression deformation of 15, 30, 50 % was carried out. It is shown that at the initial stage (ε = 15 %), the main strengthening factor of the steel under study is the presence of lamellar pearlite grains, and at high degrees of deformation (ε = 50 %), hardening by incoherent particles of the carbide phase. The overall yield strength of steel was estimated in the first approximation, based on the additivity principle, which assumes the independent action of each of the hardening mechanisms. A good qualitative agreement between the experimentally obtained and theoretically calculated values of steel strength has been revealed.

Influence of High-Temperature Annealing of Aluminum Alloys AMg6 and V95 on Their Structural-Phase State and Strength Properties

Influence of High-Temperature Annealing of Aluminum Alloys AMg6 and V95 on Their Structural-Phase State and Strength Properties

CHANGES IN THE STRUCTURAL-PHASE STATE AND DISLOCATION DENSITY OF TI49.8NI502 ALLOY DEPENDING ON THE ISOCHRONOUS ANNEALING TEMPERATURE AFTER SEVERE PLASTIC DEFORMATION BY ABC PRESSING AT 573 K

X-ray diffraction studies were conducted to examine changes in the structural-phase state and dislocation density of Ti498Ni50.2 alloy depending on the isochronous annealing temperature after severe plastic deformation by abc pressing at 573 K. The total true strain achieved in the alloy samples during abc pressing was e = 9.55. Isochronous annealing was carried out for 1 hour at 573, 673, 773, 873 and 973 K. Room-temperature analysis of all studied samples revealed the coexistence of R and B19' phases, whose relative fractions varied with annealing temperature. The high-temperature B2 phase was not detected. It was found that the most rapid decrease in the dislocation density, which was measured at 393 K (in the B2 state), occurs after annealing the samples at 673 and 773 K. After annealing at 773 K, the dislocation density reaches a minimum, and its value decreases by more than an order of magnitude compared to the value immediately after abc pressing. In the same temperature range there is a significant decrease in the root-mean-square B2 lattice microdistortions (e2)1/2 and a slight increase in the average size of coherent scattering regions. After abc pressing and after isochronous annealing, the main contribution to the physical peak broadening is made by the B2 lattice microdistortions, while the contribution from coherent scattering regions is insignificant. The obtained results show that intense recrystallization in Ti49 8Ni50.2 alloy after abc pressing at 573 K begins at T > 773 K.

Study of the structure and mechanical properties of composites used in the oil and gas industry

<abstract> <p>This article describes the structure and properties of the developed hybrid composite Hastelloy X (NiCrFeMo)-AlMoNbTaTiZr-cBNSiCNiAlCo. The composite was obtained by the high velocity oxygen fuel spraying (HVOF) method in a protective atmosphere with a subsequent high-temperature thermomechanical treatment. In order to obtain new information about the structure, we studied the metallophysical properties of the composite using electron microscopy and X-ray diffraction analysis, as well as the mechanical properties and phase composition. We studied the influence of high-energy mechanical processing of high-entropic and ceramic materials on the structural-phase state and composite quality. We determined the optimal technological parameters of HVOF in a protective atmosphere, followed by a high-temperature thermomechanical treatment. Additionally, we optimized these parameters to form a hybrid composite providing the highest adhesion and low porosity. Moreover, we investigated the microhardness of the composite layers. On the basis of complex metallophysical studies, we examined the composite formation. In order to determine the endurance limit in comparison to various other composite materials, we carried out cyclic endurance tests of the developed materials.</p> </abstract>