Phase Inclusions Research Articles

Effect of Radial-Shear Rolling on the Structure and Hardening of an Al-8%Zn-3.3%Mg-0.8%Ca-1.1%Fe Alloy Manufactured by Electromagnetic Casting.

Aluminum alloys are one of the most common structural materials. To improve the mechanical properties, an alloy of the Al-Zn-Mg-Ca-Fe system was proposed. In this alloy, when Fe and Ca are added, compact particles of the Al10CaFe2 compound are formed, which significantly reduces the negative effect of Fe on the mechanical properties. Because of the high solidification rate (about 600 K/s) during cylindrical ingot (~33 mm) production, the electromagnetic casting method (ECM) makes it possible to obtain a highly dispersed structure in the cast state. The size of the dendritic cell is ~7 μm, while the entire amount of Fe is bound into eutectic inclusions of the Al10CaFe2 phase with an average size of less than 3 μm. In this study, the effect of radial shear rolling (RSR) on the formation of the structure and hardening of the Al-8%Zn-3.3%Mg-0.8%Ca-1.1%Fe alloy obtained by EMC was studied. Computer simulation of the RSR process made it possible to analyze the temperature and stress-strain state of the alloy and to select the optimal rolling modes. It was shown that the flow features during RSR and the severe shear strains near the surface of the rod (10 mm) provided a refining and decrease in the size of the initial Fe-containing particles.

Strain stiffening elastomers with swelling inclusions.

Inhomogeneously swollen elastomers are an emergent class of materials, comprising elastic matrices with inclusion phases in the form of microgel particles or osmolytes. Inclusion phases can undergo osmotically driven swelling and deswelling over orders of magnitude. In the swollen state, the inclusions typically have negligible Young's modulus, and the matrix is strongly deformed. In that regime, the effective mechanical properties of the composite are governed by the matrix. Laying the groundwork for a generic analysis of inhomogeneously swollen elastomers, we develop a model based on incremental mean-field homogenization of a hyperelastic matrix. The framework allows for the computation of the macroscopic effective stiffness for arbitrary hyperelastic matrix materials. For an in-depth quantification of the local effective stiffness, we extend the concept of elastic stiffness maps to incompressible materials. For strain-stiffening materials, stiffness maps in the swollen state highlight pronounced radial stiffening with a non-monotonic change in stiffness in the hoop direction. Stiffening characteristics are sensitive to the form of constitutive models, which may be exploited in the design of hydrated actuators, soft composites and metamaterials. For validation, we apply this framework to a Yeoh material, and compare to recently published data. Model predictions agree well with experimental data on elastomers with highly swollen embedded microgel particles. We identify three distinct regimes related to an increasing degree of particle swelling: first, an initial decrease in composite stiffness is attributed to particle softening upon liquid intake. Second, dilute particle swelling leads to matrix stiffening dominating over particle softening, resulting in an increase in composite stiffness. Third, for swelling degrees beyond the dilute limit, particle interactions dominate further matrix stiffening.

Homogenization approach for estimating the effective thermal conductivity of Lightweight Expanded Polystyrol Concrete

This paper aims to determine the macroscopic thermal conductivity coefficient of Lightweight Expanded Polystyrene Concrete (LEPS-C) using the homogenization approach through analytical calculations. The influence of expanded polystyrene on the overall thermal conductivity coefficient of LEPS-C was determined using classical homogenization models based on the solution of the Eshelby problem, with the matrix phase being concrete and the inclusion phase being expanded polystyrene particles randomly distributed in the matrix phase. The content of substituted expanded polystyrene particles was varied from 0% to 40% by volume of concrete. The analytical calculation results obtained from the homogenization models were compared with the experimental results, showing good agreement and demonstrating the efficacy of the homogenization method in predicting the macroscopic thermal conductivity of LEPS-C.

Conceptual principles of roll casting-rolling of high-strength aluminum alloys

This paper presents the results showing the possibility of obtaining thin-sheet billets from a wide range of aluminum alloys by the method of two-roll casting. In the course of the research, an analysis of the technological solutions of the currently known methods of continuous casting and rolling of sheet metal products was performed. At the laboratory installation of two-roll casting of metals, physical and technological parameters (temperature and speed of casting, intensity of heat removal, etc.) have been worked out, which ensure a stable process of obtaining a sheet billet of small thickness (1-5 mm) from the investigated aluminum alloys. For the first time in metallurgical practice, cast sheet billets from wide-interval aluminum alloys EN2024 (Д16) (≥130 °С) and EN7075 (В95) (≥160 °С) were obtained by the roll casting method In the course of research to determine the evolution of the structures of test samples from the studied alloys, their metallographic studies were carried out at all stages of the technological chain "roll casting + hot rolling + heat treatment". Taking into account that there is a hereditary relationship between the primary structure of the cast billets and the quality of the final metal product, it was established that for all studied aluminum alloys, the basis of the structures at the "roll casting" stage is the a-phase. It was established that at the cooling rate characteristic of roll casting, the a-phase in the cast billets has a homogeneous fine-grained structure. At the same time, small inclusions of dispersed intermetallic and eutectic phases, which are present in the structure of cast billets, are evenly distributed along their cross-sections. In order to evaluate the processes occurring in the billets at the "hot rolling" stage, the patterns of changes in the quantitative characteristics of the structures depending on the degree of their deformation were determined, namely: E is the proportion of intermetallic phases; D is the size of intermetallic crystals; A is shape parameter of intermetallics; R is the size of dendritic cells; Ar is a shape parameter of dendritic cells. It was also established that at the stage of "heat treatment" of the test samples after their hot rolling, partial recrystallization of the a-Al solid solution occurs, as well as a decrease in the content of intermetallics and spheroidization of the remaining intermetallic phases. Ultimately, the changes occurring in the structures of the experimental samples had a positive effect on the quality of the final tape, which was confirmed by a relatively higher level of their mechanical characteristics.

Effect of orientation of NiSb needle inclusions on temperature dependence of resistance in Cd-=SUB=-0.95-=/SUB=-Ni-=SUB=-0.05-=/SUB=-Sb crystals

A composite Cd0.95Ni0.05Sb crystal consisting of CdSb and NiSb inclusions was obtained by the modified Bridgman method. It was shown by the methods of scanning electron microscopy, X-ray phase analysis, energy-dispersive X-ray spectroscopy, and studies of Raman spectra, that the main CdSb matrix was a block single crystal (orthorhombic Pbca structure) containing microcrystalline acicular inclusions of the second NiSb phase (hexagonal structure of the NiAs type P63/mmc). It has been found that the anisotropy of single-crystal NiSb needles in samples of the Cd0.95Ni0.05Sb crystalline composite (needles are directed along and across the current direction) significantly affects the resistance and magnetoresistance of the crystal. The interface is a needle-like inclusion --- the matrix can become superconducting, which affects the conductivity of the composite as a whole. However, this superconductivity is insufficient for the transition at the experimental temperatures to the superconducting phase with zero resistance of the composite. Keywords: cadmium antimonide, nickel antimonide, composite, anisotropy of conductivity, interface superconductivity.

Metal-Sulfide Liquation Of Ore-Forming Melt In The Fe–Fe(NiCu)S–C System And Its Role In The Genesis Of Magmatic Sulfide Deposits In The Norilsky Region (By Experimental And Geological Data)

The results of an experimental study of the melting of a graphite-saturated Fe–Fe(CuNi)S–C system at 0.5 GPa and 1150–1250°С with the addition of impurity elements Ag, Au, Re, Pt, Pd, and Rh are presented. The quenched sulfide melt forms the matrix of the sample, at 1150–1200°С it is represented by the FeNiS pyrrhotite phase (Mss) with inclusions of the FeCuS phase (Iss) anomalously enriched in Cu. At 1250°С, the sulfide melt is quenched in the form of a homogeneous pyrrhotite Ms phase of the Fe(CuNi)S composition. The change in the Ms composition of the quenched sulfide melt by the two-phase Mss + Iss association is considered as evidence of the existence of supra-liquidus Mss and Iss stratification of the sulfide Fe–Ni–Cu melt in the range of 1150–1250°С. As a result of fractionation of elements between immiscible Fe-sulfide (Ms) and Fe-metal (Mc) melts, Fe, Ni, Pt, Re, Au are predominantly concentrated in the metal melt, while Cu, Ag are concentrated in the sulfide melt. The role of the supra-liquidus Mss–Iss liquation in the genesis of sulfide mineralization of the deposits of the Talnakh ore cluster, including pyrrhotite-chalcopyrite "drops" in picritic gabbro-dolerites, as well as pyrrhotite and chalcopyrite types of ores of zonal sulfide deposits, is discussed. The role of Ms and Mc separation of the Fe-sulfide melt during carbon contamination in the Cu–Pd specialization of magmatic sulfide deposits of the Norilsk region is considered.

Влияние ориентации игольчатых включений NiSb на температурную зависимость сопротивления в монокристаллах Cd-=SUB=-0.95-=/SUB=-Ni-=SUB=-0.05-=/SUB=-Sb

A composite Cd0.95Ni0.05Sb crystal consisting of CdSb and NiSb inclusions was obtained by the modified Bridgman method. It was shown by the methods of scanning electron microscopy, X-ray phase analysis, energy-dispersive X-ray spectroscopy, and studies of Raman spectra, that the main CdSb matrix was a block single crystal (orthorhombic Pbca structure) containing microcrystalline acicular inclusions of the second NiSb phase (hexagonal structure of the NiAs type P63/mmc). It has been found that the anisotropy of single-crystal NiSb needles in samples of the Cd0.95Ni0.05Sb crystalline composite (needles are directed along and across the current direction) significantly affects the resistance and magnetoresistance of the crystal. The interface is a needle-like inclusion - the matrix can become superconducting, which affects the conductivity of the composite as a whole. However, this superconductivity is insufficient for the transition at the experimental temperatures to the superconducting phase with zero resistance of the composite.

The Effect of La on the Microstructure and Mechanical Properties of the (Al) + Al4(Ca,La) Wrought Alloys

This article is devoted to optimization of the chemical composition of the high-tech Al–3 wt %Ca–(0.5–2.0) wt % La–1.5 wt % Mn alloys. The perspective of a decrease in the content of lanthanum from 2 to 0.5 wt % in new alloys has been validated using advanced methods for analyzing the structure and phase composition (electron microscopy, X-ray phase analysis, thermodynamic calculation) and using the analysis of mechanical (tensile) properties formed in the course of deformation treatment. The evolution of the struc-ture of the alloys was studied in the course of thermodeformation treatment. It has been shown that upon hot rolling at 400°С with no preliminary annealing of ingots it is possible to obtain high-quality deformed semiproducts (sheets) with no surface and edge defects (up to a 90% reduction). The deformation treatmentprovides the formation of a structure with inclusions of a (Al,Mn)4(Ca,La) eutectic phase uniformly distrib-uted in an aluminum matrix and found in a form of ring-shaped precipitates of submicron sizes (300 × 150 nm). In addition, the formation of a net of low-angle boundaries (subgrains) with a mean size of ~1 μm is observed; some inclusions of a eutectic phase are found along these boundaries. This combination of struc-tural characteristics mainly determines the ability of reaching favorable mechanical properties of an alloy after hot rolling with 0.5 wt % La (the ultimate strength of 240–260 MPa, yield strength of 185–205 MPa, and rel-ative elongation of 5.5–9.0%), which are comparable with the properties of the previously studied alloy with up to 2 wt % La.

Исследование динамической прочности мелкозернистого оксида алюминия, полученного методом электроимпульсного плазменного спекания

The results of dynamic compressive testing of alumina samples with different grain sizes sintered from nano and fine α-Al2O3 powders are presented. The ceramics were obtained by spark plasma sintering (SPS). The effect of heating rate (Vh), sintering temperature (Ts), holding time (ts), cooling rate (Vc) on hardness, fracture toughness, dynamic strength stress (σY) of Al2O3 has been studied. An amorphous layer of nanometer thickness was present on the surface of nanopowders in the initial state. After sintering, the grain boundaries of the ceramics had a crystalline structure; no inclusions of the amorphous phase were found. It has been suggested that during the SPS process, an amorphous structure containing an excess free volume is transformed into a crystalline phase with the formation of dislocation-type defects at the grain boundaries, which create long-range internal stress fields. It is shown that nanopores less than 50 – 100 nm in size are present at the grain boundaries of sintered ceramics. It is shown that the nonmonotonic nature of the dependence of σY on the temperature and time of the SPS is due to the simultaneous change in the density, the nonequilibrium state of the grain boundaries, and the grain size of the ceramic. It is shown that a decrease in the degree of nonequilibrium of the grain boundaries of alumina due to an increase in the SPS temperature or an increase in the holding time makes it possible to increase the dynamic strength of alumina. It has been established that an increase in the cooling rate leads to the formation of compressive residual stresses and a slight increase in σY of ceramics. The maximum dynamic strength (σY = 1755 MPa) for alumina ceramics with average grain size 1.6 – 2 µm obtained by SPS (Vh = 50 °С/min, Ts = 1520 °С, ts = 50 min).

Структура и свойства биоинертного покрытия Mo – Nb, сформированного на медицинском сплаве Titanium Grade 5 электровзрывным методом

In this article, an attempt was made to solve the problem of creating a coating for an implant that has better biological compatibility than the medical titanium alloy Titanium Grade 5. A Mo – Nb coating of the composition Mo – Nb is formed on the titanium grade 5 medical alloy by the electroexplosive method. The coating is formed as a result of the simultaneous electric explosion of molybdenum and niobium foils. A set of studies has been carried out to establish the structure, phase composition, and properties of the formed coatings. The coatings were studied by scanning and transmission electron microscopy. It is shown that the hardness of the surface layer of the coating by 60 % and Young’s modulus by 43 % exceed the corresponding characteristics of the Titanium Grade 5 alloy. The thickness of the layer with high (relative to the substrate) values of hardness and Young’s modulus reaches 80 µm. It was found that the wear parameter of the coating is 1.8 times, and the friction coefficient of the coating is 1.6 times higher than the wear parameter and the friction coefficient of the substrate. It has been established that in the surface layer, along with the coating atoms, there are Al, Ti, V atoms, which indicates that the coating is doped with substrate atoms, as well as oxygen and carbon atoms. The layering of the coating by elemental composition was revealed, namely, the top of the coating is enriched with niobium atoms, the lower part of the coating is enriched with molybdenum atoms. It is shown that the coating has a polycrystalline structure formed by a solid solution based on molybdenum. In the bulk and along the grain boundaries, there are inclusions of the second phase of the composition a-Ti, Nb, Mo9Ti4, and NbTi4 of various shapes and sizes. The studies of the phase composition did not reveal compounds based on vanadium and aluminum, which reduce the biocompatibility of the coatings. The identified phases contain only molybdenum, niobium and titanium, which are bioinert. This fact suggests that, as in studies of the phase composition of the surface of the coatings and its change in thickness, the biocompatibility of the obtained coatings will be higher compared to the Titanium Grade 5 titanium alloy. The conducted complex of studies makes it possible to recommend the resulting coatings for further clinical trials. These coatings are expected to be used in the future for better survival of titanium implants in the human body.

ИССЛЕДОВАНИЕ СТРУКТУРЫ СПЛАВОВ СИСТЕМ Al‒Si,Mn‒Fe‒CoМЕТОДАМИ СКАНИРУЮЩЕЙ ЭЛЕКТРОННОЙ МИКРОСКОПИИ

Scanning electron microscopy (SEM) is one of the widely used modern microscopic techniques designed to obtain visual information about the microstructure of solid-phase objects (alloys, metals, etc.). The paper presents the areas of application of a scanning electron microscope (semiconductors; biology and medicine; chemical, petrochemical, mining industries; research laboratories). Examples of analysis of various structures of materials (high-entropy alloy, silumin, fracture structure of A5M aluminum alloy) obtained using the scanning electron microscope method are given. It is shown that rounded pores (1.3±0.1 µm) are present in the microstructure of the high-entropy alloy of the Mn-Fe-Co-Cr-Ni system. The reason for the formation of pores may be the specifics of the wire-arc additive manufacturing technology. The structure of the silumin of the AL-10%SI system demonstrates a multiphase, morphologically diverse character. Irradiation with an electron beam of silumin is accompanied by melting of aluminum along the interfaces with inclusions of the second phase. The fracture of an A5M aluminum sample destroyed under fatigue conditions has an ash-gray color and a highly rough matte surface. As a result of studying the deformation characteristics of commercially pure A5M aluminum, it was found that samples of commercially pure aluminum in the initial state reach critical deformation and fail on average at 18742±654 cycles. The use of a magnetic field of 0.1 T of constant geometry leads to an increase in the number of cycles to failure by 36.8%, on ave-rage, the samples are destroyed at 25207±2349 cycles.

Identifying Oxide and CaS Non-Metallic Inclusions in Steel with Raman Spectroscopy

Identification and characterization play an essential role in the study of non-metallic inclusions (NMIs) in monitoring the steel casting process and product quality. This study uses Raman spectroscopy, a versatile, relatively fast, and non-destructive technique for characterizing oxide and sulfide-based inclusion phases in steel samples. The relative Raman peak intensities and positions were used to qualitatively estimate the inclusion phases of Al2O3, CA, C12A7, C3A, MgO·Al2O3, and CaS. For a quantitative estimation, FESEM-EDS (field emission scanning electron microscope with energy dispersive X-ray spectroscopy) was used to evaluate the inclusion phases in the samples. This study demonstrates that Raman spectroscopy can be used to rapidly estimate the content of Al2O3, magnesium aluminate spinel (MgO·Al2O3), and the calcium aluminate phases of CA, C3A, and C12A7 in steel samples to complement established characterization techniques for NMIs analysis such as FESEM-EDS.

Petrogenetic history and melt inclusion characteristics of mantle plume-derived ijolites from NE India: implications for multistage crystallization and occurrence of “nano-calciocarbonatites”

The Sung Valley ultramafic–alkaline–carbonatite complex (UACC) of Meghalaya, NE, India, is a result of magmatic activity related to the Kerguelen mantle plume spanning from 101 to 115 Ma. In the present study, an integrated crystal size distribution (CSD), mineral chemistry, and melt inclusion analysis are carried out on the ijolites present within this UACC. The CSD analysis shows that these ijolites were formed in multiple stages through changes in the crystallization environment, such as cooling and nucleation rates. Raman spectroscopy of mineral inclusions of rutile, aphthitalite, apatite, carbonate–silicate melt inclusions, and disordered graphite within clinopyroxene and titanite, respectively, indicates a heterogeneous composition of the parental magma. These mineral and melt inclusion phases further suggest localized changes in oxygen fugacity (fO2) due to redox reactions in the lower crust. SEM–EDX analysis of the exposed melt inclusions reveals the presence of alkali-bearing diopside, phlogopite, and andradite, along with an unidentified carbonated silicate daughter phase. The studied melt inclusions are dominated by carbonate, whereas silicates are subordinate. The presence of this fully crystallized carbonate–silicate melt as calcite, diopside, phlogopite, magnetite, apatite, and andradite suggests the presence of “nano-calciocarbonatites” in these ijolites. Our study provides insights into different mechanisms of the loss of alkalies from initially entrapped alkaline carbonate melt in clinopyroxenes. The predominant occurrence of calcite as the only carbonate phase in the studied melt inclusions is a result of silicate–carbonate melt immiscibility, calcite-normative system in these inclusions, dealkalization of the alkaline carbonates in the presence of external fluid, and/or redistribution of the alkalies to the daughter alkali-bearing silicates.

Carrier Mobility Modulation in Cu2Se Composites Using Coherent Cu4TiSe4 Inclusions Leads to Enhanced Thermoelectric Performance

Carrier transport engineering in bulk semiconductors using inclusion phases often results in the deterioration of carrier mobility (μ) owing to enhanced carrier scattering at phase boundaries. Here, we show by leveraging the temperature-induced structural transition between the α-Cu2Se and β-Cu2Se polymorphs that the incorporation of Cu4TiSe4 inclusions within the Cu2Se matrix results in a gradual large drop in the carrier mobility at temperatures below 400 K (α-Cu2Se), whereas the carrier mobility remains unchanged at higher temperatures, where the β-Cu2Se polymorph dominates. The sharp discrepancy in the electronic transport within the α-Cu2Se and β-Cu2Se matrices is associated with the formation of incoherent α-Cu2Se/Cu4TiSe4 interfaces, owing to the difference in their atomic structures and lattice parameters, which results in enhanced carrier scattering. In contrast, the similarity of the Se sublattices between β-Cu2Se and Cu4TiSe4 gives rise to coherent phase boundaries and good band alignment, which promote carrier transport across the interfaces. Interestingly, the different cation arrangements in Cu4TiSe4 and β-Cu2Se contribute to enhanced phonon scattering at the interfaces, which leads to a reduction in the lattice thermal conductivity. The large reduction in the total thermal conductivity while preserving the high power factor of β-Cu2Se in the (1-x)Cu2Se/(x)Cu4TiSe4 composites results in an improved ZT of 1.2 at 850 K, with an average ZT of 0.84 (500-850 K) for the composite with x = 0.01. This work highlights the importance of structural similarity between the matrix and inclusions when designing thermoelectric materials with improved energy conversion efficiency.

Evolution of the grain structure of metals and alloys under intense plastic deformation: multilevel models

It is well known that the performance properties of products made of metals and alloys are determined mainly by the meso- and microstructure of the latter. The structure of materials is formed and undergoes significant changes in the processes of manufacturing parts and structures using thermomechanical processing methods. A very important parameter that determines the physical and mechanical characteristics of materials is the grain structure (size, shape, relative positions of grains and inclusions of various phases). In recent decades, in this regard, special attention has been paid to the processes of severe plastic deformation (SPD), which make it possible to obtain a submicro- and nanocrystalline grain structure, which provides a significant increase in the performance properties of products made of metals and alloys. The development of SPD technologies in modern conditions is unthinkable without mathematical modeling of the processes under consideration; the most important component in the development of such a "toolkit" are constitutive relations (or, more broadly, constitutive models). In connection with the foregoing, the latter should be able to describe the evolutionary structure at various scale levels. Until now, the practice of developers of materials processing technologies has been dominated by the use of macrophenomenological models based on classical continuum theories of plasticity, viscoplasticity, and creep. From the second half of the 20th century to the present, various improvements to the constitutive models of the above class have been proposed, in which additional parameters and kinetic equations are introduced for them, describing certain characteristics of the structure of materials. As a rule, such models make it possible to obtain an adequate picture of the changing structure, however, for specific materials and methods of thermomechanical treatment. At the same time, such models, unfortunately, do not have the necessary universality; when changing the material or processing method, they have to be significantly “customized” to specific conditions, up to a complete change in the relationships included in the model. A brief review of works devoted to the creation and application of models of this class is given in the previous article by the authors. The most promising and possessing a significant degree of universality, according to the authors, are currently multilevel constitutive models based on the introduction of internal variables and physical theories of plasticity (elastoviscoplasticity). A review of works that consider various aspects of the formulation, modification, numerical implementation and application of such models is proposed in this article. The main attention is paid to models focused on the description of changes in the structure of materials due to dislocation-disclination mechanisms; a brief note is given on models that take into account thermally activated diffusion mechanisms, due to which the processes of recovery and recrystallization are realized.

High-entropy Fe-Cr-Ni-Co-(Cu) coatings produced by vacuum electro-spark deposition for marine and coastal applications

High-entropy coatings (HECs) are of a great interest for the protection of structural steels and alloys used in the costal and offshore areas. Here, thick, dense, and uniform Fe-Cr-Ni-Co-(Cu) coatings with a crack-free surface have been successfully deposited on AISI 420S steel by vacuum electro-spark deposition using CrNiCo and CrNiCoCu electrodes. The coatings consist of columnar grains (approximately 300 nm in diameter) and subgrains (10–50 nm thick) of an fcc phase and spherical inclusions of mixed SiO2 + (Cr,Ti)2O3 oxide, 30–50 nm in size. Although Cu is an element prone to segregation, the experimental results show that Cu does not form its own phase and is in the metal solid solution. Molecular dynamics simulation shows that Cu has a slight tendency to self-clustering and form Cu-rich clusters in FeCrNiCo-Cu HECs. However, several regions enriched in Cu are observed in the FeCrNiCo-Cu samples. FeCrNiCo coatings tested in artificial seawater and the Black Sea exhibited enhanced corrosion resistance. In tribocorrosion tests, FeCrNiCo-(Cu) coatings performed better than steel substrate due to faster recovery of a passive film. The addition of Cu has a positive effect on the antibacterial activity of FeCrNiCo coatings against Gram-positive B. cereus Arc30 and B. cereus F strains.

The Electrical Resistivity of Multiphase Systems Based on the Ti3AlC2 Hexagonal Phase at Low Temperatures

The electrical resistivity of three samples is measured in the range 4.2–295 K. One sample contains the pure Ti3AlC2 MAX‐phase, and the other two samples contain this phase together with inclusions of TiC, TiO, and Al2O3 phases. To estimate the value of the residual resistivity of the TiC phase, data of energy‐dispersive X‐ray spectroscopy concentration distributions of elements are used. Estimations show that the Ti3AlC2 phase has the smallest residual resistivity of all phases and can electrically shunt other phases. The approximation of temperature dependences of the resistivity reveals that the Bloch–Grüneisen term of scattering of electrons on phonons (i.e., the term proportional to T5) increases strongly with the increase of volume fractions of inclusions. According to the proposed explanation of this effect, interstitial impurities of the carbon in the Ti3AlC2 phase migrate to neighbor crystals of the titanium carbide during the formation of the MAX phase, so the purification of this phase from carbon appears. As all other phases are electrically shunted by the Ti3AlC2 phase, the Bloch–Grüneisen term of the resistivity of this purified Ti3AlC2 phase increases.

Bearing Aluminum-Based Alloys: Microstructure, Mechanical Characterizations, and Experiment-Based Modeling Approach.

Due to the engine's start/stop system and a sudden increase in speed or load, the development of alloys suitable for engine bearings requires excellent tribological properties and high mechanical properties. Including additional elements in the Al-rich matrix of these anti-friction alloys should strengthen their tribological properties. The novelty of this work is in constructing a suitable artificial neural network (ANN) architecture for highly accurate modeling and prediction of the mechanical properties of the bearing aluminum-based alloys and thus optimizing the chemical composition for high mechanical properties. In addition, the study points out the impact of soft and more solid phases on the mechanical properties of these alloys. For this purpose, a huge number of alloys (198 alloys) with different chemical compositions combined from Sn, Pb, Cu, Mg, Zn, Si, Ni, Bi, Ti, Mn, Fe, and Al) were cast, annealed, and tested for determining their mechanical properties. The annealed sample microstructure analysis revealed the formation of soft structural inclusions (Sn-rich, Sn-Pb, and Pb-Sn phases) and solid phase inclusions (strengthened phase, Al2Cu). The mechanical properties of ultimate tensile strength (σu), Brinell hardness (HB), and elongation to failure (δ) were used as control responses for constructing the ANN network. The constructed network was optimized by attempting different network architecture designs to reach minimal errors. Besides the excellent tribological characteristics of the designed set of alloys, soft inclusions based on Sn and Pb and solid-phase Cu inclusions fulfilled the necessary level of mechanical properties for anti-friction alloys; the maximum mechanical properties reached were: σu = 197 ± 7 MPa, HB = 77 ± 4, and δ = 20.3 ± 1.0%. The optimal ANN architecture with the lowest errors (correlation coefficient (R) = 0.94, root mean square error (RMSE) = 3.5, and average actual relative error (AARE) = 1.0%) had two hidden layers with 20 neurons. The model was validated by additional experiments, and the characteristics of the new alloys were accurately predicted with a low level of errors: R ≥ 0.97, RMSE = 1-2.65, and AARE ˂ 10%.

FEATURES OF THE CRACKS’ FORMATION IN HETEROPHASE INCLUSIONS OF THE “EUTECTICS OF INCLUSION – MATRIX” TYPE

The purpose of the article − to study of crack nucleation features in heterophase inclusions of the “eutectic of inclusion-matrix” type during steel deformation. Methods. The research was conducted after deformation for a number of different grades steel samples in the temperature range of 20...1 200 °С on Instron-1195 and IMASH-5C with special grippers, with a gripper movement speed of 1 680 mm/min. Research methods were used: petrography, micro-X-ray spectral analysis (Cameca MS-4, Nanolab-7), optical microscopy (Neophot-21). Results. It is found that the variety of phases composing the heterophase inclusions of the "eutectic of inclusion-matrix" type leads to their different behaviour under conditions of plastic deformation. It is shown that the nucleation of brittle or viscous microcracks occurs along the internal interfacial boundaries between the metal matrix and the second phase of the eutectic. It is defined that the cracks’ nature is determined by the plasticity level of the inclusion phases and the deformation temperature. It is shown that the critical degrees of samples’ deformation, at which appreciable microcracks along the internal interphase boundaries appeared, depend on the temperature and the nature of the inclusion phase “eutectic of inclusion – matrix”. It is found that the values of deformation critical degrees determine the level of cohesive strength for internal interphase boundaries in heterophase inclusions “eutectic of inclusion – matrix”. Scientific novelty. The features of microcracks nucleation in heterophase inclusions of the “eutectic of inclusion − matrix” type are determined. It is shown that the nature of the microcracks formed along the interphase boundaries depends on the temperature, plasticity level and combination conditions of brittle and plastic phases in inclusions of the “eutectic of inclusion − matrix” type as well as on the deformation temperature. It is shown that the critical degrees of steels deformation, when microcracks appeared along the internal interphase boundaries, determine the cohesive strength of these boundaries and depend on the temperature and the nature of the inclusion phase “eutectic of inclusion − matrix” type. Practical value. The use of the obtained results will make it possible to develop technologies for producing steels with regulated types of non-metallic heterophase inclusions that will allow to increase considerably their technological and operational characteristics, and also to prevent the formation of various defects during steel pressure treatment and product operation.

FEATURES OF THE CRACKS’ FORMATION IN HETEROPHASE INCLUSIONS OF THE “DISPERSED PHASES IN A NON-METALLIC MATRIX” TYPE

The purpose of the article − to study of crack nucleation features in heterophase inclusions of the “dispersed phases in a non-metallic matrix” type under the conditions of steels’ plastic deformation. Methods. The research was conducted after deformation for a number of different grades steel samples in the temperature range of 20...1 200 °С on Instron-1195 and IMASH-5C with special grippers, with a gripper movement speed of 1 680 mm/min. Research methods were used: petrography, micro-X-ray spectral analysis (Cameca MS-4, Nanolab-7), optical microscopy (Neophot-21). Results. It is shown that the variety of phases composing the heterophase inclusions "dispersed phases in non-metallic matrix" leads to their different behaviour under plastic deformation conditions. At the same time, the nucleation of brittle or viscous microcracks occurs along the internal interphase boundaries between the "non-metallic" matrix and the dispersed particles of the second phase. The cracks’ character near the inclusions determined by the plasticity level of “matri” and dispersed phases of inclusions and the deformation temperature are revealed. The determined critical degrees of samples’ deformation, upon reaching which appreciable microcracks along the internal interphase boundaries occurred, were depend on temperature and the nature of the “dispersed phases in a non-metallic matrix” inclusions. Scientific novelty. The features of microcracks nucleation associated with heterophase inclusions of the “dispersed phases in non-metallic matrix” type with different combination of brittle and plastic phases during steels’ deformation are determined. The types of microcracks occurring in inclusions of the “dispersed phases in the non-metallic matrix” type and the locations of their formation have been determined. It is shown that the values of the deformation critical degrees determine the level of cohesive strength for internal interphase boundaries in heterophase inclusions “dispersed phases in a non-metallic matrix” at different deformation temperatures. Practical value. The use of the obtained results will make it possible to develop technologies for producing steels with regulated types of non-metallic heterophase inclusions that will allow to increase significantly their technological and operational characteristics, and also to prevent the formation of various defects in the steels' treatment by pressure and the operation of products.