Formation Of Surface Layer Research Articles

THERMAL CALCULATIONS OF RAPID HEATING AND COOLING DURING TESTING THE TECHNOLOGY OF COMBINED SURFACE HARDENING OF WELDED PARTS WITH A WORKING PART MADE OF 15X11MF STEEL

Hardening of contacting surfaces is aimed at improving the material properties of components to ensure more efficient operation of mechanisms and devices. There are many surface modification technologies, such as: creating surfacing on the surface, creating coatings, forming surface layers using various techniques, and other technologies. Such technologies are aimed at improving the mechanical and tribological properties of materials and products made of them. Combined surface hardening using friction is a hardening method that can significantly improve the mechanical and tribological properties of materials. Thermal calculations of the process are an important aspect for controlling this hardening method. In this regard, there is an urgent need to perform thermal calculations of the process of rapid heating and cooling after heating during testing the technology of combined surface hardening of welded parts. the purpose of this work is to perform thermal calculations of the cycle of rapid heating and cooling after heating during surface hardening of welded parts with a working part made of 15X11MF steel. This steel grade is a structural alloy steel with increased corrosion resistance. Combined surface hardening was performed on a friction treatment unit. The source of heating in the combined surface hardening technology is the friction that occurs between the tool, a rotating steel disk, and the surface of the workpiece. To analyze the temperature distribution from the surface deep into the samples during combined surface hardening, the heat conduction problem was solved using the source method. The problem of heat conduction was solved in a coordinate system that moves with the heat source, i.e., with the contact surface The input parameters for calculating thermal phenomena during the combined surface hardening of the studied material were: a - thermal conductivity coefficient; λ - thermal conductivity coefficient; аф - actual value of the machining depth taken from the side where the microgroove was made; r is the radius of the disk; L is the length of contact between the disk and the sample surface during sample processing; y is the heat source criterion - the isotherm value of 150 °C, taken from the side where the grinding was performed. The result of thermal calculations according to the shape of the source is the temperature field from an instantaneous source of the corresponding shape. The temperature field is shown in the boundary plane of the sample plate section and demonstrates to what depth and temperature the sample was heated during processing To evaluate and analyze the thermal cycle of steel heating and cooling during machining, a corresponding heating-cooling graph was calculated and plotted, which makes it possible to calculate the actual cooling rate in the surface layer of the samples during machining. The expediency of applying this technology in terms of a high-speed method of heating and cooling the surface layer of the processed parts is shown. The data obtained make it possible to calculate the cooling rate of the surface after heating in the process of combined surface hardening, or the cooling rate at any depth of the part sample within the temperature field that occurs during its processing, which is planned infurther research.

Improving the Wear and Corrosion Resistance of Titanium Alloy Parts via the Deposition of DLC Coatings

This article compares the properties of the diamond-like carbon (DLC) coating with those of ZrN and (Zr,Hf)N coatings deposited on the Ti-6Al-4V titanium alloy substrate. To improve substrate adhesion during the deposition of the DLC coating, preliminary etching with chromium ions was conducted, ensuring the formation of a chromium-saturated diffusion surface layer in the substrate. A Si-DLC layer followed by a pure DLC layer was then deposited. The hardness of the coatings, their surface morphology, fracture strength in the scratch test, and tribological properties and wear resistance in the pin-on-disk test in contact with Al2O3 and steel indenters were investigated. The structure of the DLC coating was studied using transmission electron microscopy, and its corrosion resistance in an environment simulating blood plasma was also investigated. In the pin-on-disk test in contact with Al2O3 and AISI 52100 indenters, the DLC-coated sample demonstrates a much lower friction coefficient and significantly better wear resistance compared to the nitride-coated and uncoated samples. Both nitride coatings—(Zr,Hf)N and ZrN—and the DLC coating slow down the corrosive dissolution of the base compared to the uncoated sample. The corrosion currents of the (Zr,Hf)N-coated samples are 37.01 nA/cm2, 20% higher than those of the ZrN-coated samples. The application of (Zr,Hf)N, ZrN, and DLC coatings on the Ti-6Al-4V alloy significantly inhibits dissolution currents (by 30–40%) and increases polarization resistance 1.5–2.0-fold compared to the uncoated alloy in 0.9% NaCl at 40 °C. Thus, the DLC coating of the described structure simultaneously provides effective wear and corrosion resistance in an environment simulating blood plasma. This coating can be considered in the manufacture of medical products (in particular, implants) from titanium alloys, including those functioning in the human body and subject to mechanical wear (e.g., knee joint endoprostheses).

High-temperature annealing of calcium lanthanum sulfide

Calcium lanthanum sulfide ceramic with a target at% composition of CaS: La2S3 of 10 : 90 was subjected to annealing at 1100 °C in dry nitrogen ambient. Cross-sectional scanning/transmission electron microscopy was used to understand the changes to the stoichiometry and structure of the ceramic. It was found that residual, ‘dissolved’ oxygen (up to 5.4 at%) in the annealed sample diffused outwards while sulfur was lost to the ambient and calcium diffused inwards. These diffusion processes were accompanied by the formation of a sub-µm thick surface layer of La2O2S and a sub-surface layer of La20OS29 in the calcium-free zones. The phase formation of the oxysulfides was explained within the context of existing phase diagrams of La-O-S and Ca-La-S. Reaction modeling of the diffusion processes were used to explain the sequential mechanistic steps responsible for the formation of the oxysulfides on calcium lanthanum sulfide surfaces upon annealing.

Origin of Persisting Photoresponse of One-Year Aged Two-Dimensional Lead Halide Perovskites Stored in Air under Dark Conditions.

Two-dimensional halide perovskites are promising for advanced photonic, optoelectronic, and photovoltaic applications. However, their long-term stability is still a critical factor limiting their implementation into further commercial applications. Here, we present an environmental stability analysis of BA2(MA)n-1PbnI3n+1 (BA = C4H12N+, MA = CH6N+) two-dimensional perovskites with the lowest quantum well thicknesses of n = 1 and n = 2, after 1 year of aging under ambient humidity, oxygen content, and light conditions. We observed that both crystal phases (n = 1 and 2) degraded similarly, resulting in the removal of organic components and crystal decomposition into PbI2, Pb oxides, and Pb hydroxides. However, we have found a significant difference between their aging under ambient light and dark conditions, affecting their degraded morphology and photoactivity. Both crystal phases exposed to ambient light aged into a morphology characterized by the formation of several pinholes and voids, accompanied by photoluminescence degradation. Samples stored under dark conditions surprisingly preserved their photoluminescence activity, which morphologically aged into microrod structures. We conclude that the observed loss of photoactivity of 2D perovskites aged under ambient light is attributed to photoaccelerated degradation processes causing faster crystal surface photo-oxidation accompanied by a creation of multiple I vacancies and hydration of the inner crystal. The retainment of photoactivity in 2D perovskites aged under dark conditions is attributed to slower surface oxidation processes into Pb salts, as confirmed by X-ray photoemission spectroscopy. The formed surface layer even allows for a layer-by-layer degradation and acts as a protection barrier against further additional loss of I atoms and the consequent hydration of the inner part of samples. We demonstrate that light is the most critical external factor accelerating 2D perovskite degradation processes in ambient air and thus affecting their long-term stability. We conclude in this work that perovskite material structural engineering together with their surface passivation or encapsulation strategical techniques applied is an essential step for their further application into long-term stable commercial devices.

Impact of Electrolyte Additives on the Lifetime of High Voltage NMC Lithium-Ion Pouch Cells

This work involves improving the lifetime of lithium-ion cells during high voltage cycling using electrolyte additives. Three generations of electrolyte additives were investigated and screened in NMC442/graphite pouch cells using a 24 h voltage-hold protocol at 40 °C to accelerate oxidative reactions occurring at 4.4 V. Once promising additives and combinations were identified, they were then tested in cobalt-free NMC640/graphite cells for long-term cycling to upper cutoff voltages of 4.3, 4.4, and 4.5 V at temperatures of 20, 40, and 55 °C. Degradation mechanisms were probed using dV/dQ analysis, micro-X-ray fluorescence spectroscopy, and electrochemical impedance spectroscopy. The primary failure mode of cells held at high voltages is due to increase in cell impedance, which is correlated to the dissolution of transition metals, specifically manganese, originating from the positive electrode. We believe this dissolution is presumably due to the formation of a high impedance rock salt surface layer on the NMC positive electrode particles. Such deleterious outcomes can be limited by selecting an appropriate electrolyte additive package. It is hoped that this paper can provide a starting point for developing NMC Li-ion cells that can operate to voltages as high as 4.4 V and still display long lifetimes.

Study of the chemical process of surface layer formation during plasma heating of a coating containing an alloy of the NiCrBSi system

Study of the chemical process of surface layer formation during plasma heating of a coating containing an alloy of the NiCrBSi system

Synthesis, Characterization, Theoretical, and evaluation of Eco-Friendly benzimidazolylmethyl-pyrazole carboxylate Schiff Bases corrosion inhibitors for mild steel

In this study, benzimidazolylmethyl-pyrazole carboxylate derivatives were synthesized via a 1,3-dipolar cycloaddition reaction and characterized using IR, HRMS and NMR spectroscopy. Three derivatives, namely ethyl 5-((3-(cyclohex-1-en-1-yl)-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)methyl)-1-phenyl-1H-pyrazole-3-carboxylate (Ph-BPC), ethyl 5-((3-(cyclohex-1-en-1-yl)-2-oxo-2,3-dihydro- 1H-benzo[d]imidazol-1-yl)methyl)-1-(p-tolyl)-1H-pyrazole-3-carboxylate (CH3Ph-BPC), and ethyl 1-(4-chlorophenyl)-5-((3-(cyclohex-1-en-1-yl)-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)methyl)-1H-pyrazole-3-carboxylate (ClPh-BPC), were evaluated as corrosion inhibitors for mild steel (MS) in a 1 M HCl solution. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements revealed high inhibition efficiencies of 98.5 %, 98.2 %, and 97.7 % for ClPh-BPC, Ph-BPC, and CH3Ph-BPC, respectively, at a concentration of 10-4 M. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) analyses confirmed the formation of protective surface layers, significantly reducing corrosion rates. Thermodynamic analysis indicated that the adsorption of these inhibitors follows the Langmuir isotherm model with adsorption energies of −50.12 kJ/mol for ClPh-BPC, −50.52 kJ/mol for Ph-BPC, and −51.62 kJ/mol for CH3Ph-BPC, suggesting chemisorption. Computational studies, including Monte Carlo (MC), density functional theory (DFT), and molecular dynamics (MD) simulations, showed strong agreement with experimental results, further validating the adsorption behavior and corrosion inhibition mechanisms of these compounds.

MODELING THE PLASTIC DEFORMATION STATE OF THE CONTACT SURFACE DURING FRICTION

The mechanics of contact destruction of compounds during friction under conditions of complex thermodynamic loading was researched. The possibility of a mathematical description of complex damage to friction units and wear intensity is shown, taking into account the peculiarities of the surface layer formation during contact. A method for calculating the surface strength and durability of tribo-compounds is presented. This allows us to relate the parameters of the stressed state of a point (friction coefficient, shape factor) with the thermomechanical parameters of the process. By assessing changes in the friction coefficient and shape parameters, it becomes possible to determine the yield stress and establish structural transformations corresponding to a given stress state.

Electrochemical Production of Tungsten Oxides from Wc-Co Carbide-Type Pseudo-Alloy Waste

Electrochemical research is devoted to the development of a method of processing secondary raw materials containing tungsten in the form of a pseudoalloy of the carbide type WC–Co in sulfate solutions. The target processing products are: powders of tungsten oxides of lower oxidation states, which can be reduced to metallic tungsten with lower costs. Using the methods of linear and cyclic voltammetry, it was established that the selective dissolution of the cobalt component of the pseudoalloy in the studied solutions occurs at potentials more positive than 0.2 V, carbon is removed from the working electrode at a potential > 0.8 V. At the same time, tungsten is oxidized to the higher oxide WO3. It was determined that in sulfuric acid, with an increase in its concentration from 1 to 5 mol∙dm-3, the current density decreases, which is associated with the formation of a solid surface layer of tungsten oxide on the surface of the anode, which passivates the surface. It was established experimentally that when adding 1 mol∙dm-3 of H2SO4 hexamine (C6H12N4) with a concentration of 0.9 mol∙dm-3 to a solution, it is possible to block the process of formation of a passivating film and obtain powders of tungsten oxides of lower oxidation states.

Wear and corrosion properties of low-temperature nitrocarburized 17-4PH SLM components

3D printing has demonstrated manufacturing and economic advantages in terms of customization, flexibility and rapid prototyping of precision complex geometric components. The 17-4PH precipitate hardening steel is notable for its excellent corrosion resistance. This study aims on enhancing the wear resistance of SLM-printed 17-4PH components through interstitial surface hardening. To eliminate microstructural defects introduced by the SLM process, the components were first subjected to solution heat treatment. Following this, a low-temperature nitrocarburizing (LTNC) process was applied at temperatures below 400 °C, resulting in the formation of an interstitial surface layer with an average thickness of approximately 17 μm. Optical microscopy and XRD analyses confirmed the presence of a dual-phase structure composed of expanded BCC and FCC phases within the hardened layer, with no detectable nitride/carbide precipitates. Quantitatively, the LTNC process significantly enhanced the surface microhardness of the components, increasing it to a minimum of 1000 HV0.2. The bulk microhardness also increased from 360 HV0.2 to 480 HV0.2, indicating an aging effect during the diffusion treatment. In terms of performance, LTNC substantially improved the wear resistance of the components. However, a slight reduction in corrosion resistance was observed, attributed to increased surface roughness and the presence of the dual-phase expanded structure.

Influence of Initial Film Properties in UVO-Mediated Patterning of an Elastomeric Film Using a TEM Grid.

Ultraviolet irradiation of a cross-linked polydimethylsiloxane (PDMS) Sylgard 184 film in the presence of atmospheric oxygen (UVO) through a bare transmission electron microscope (TEM) sample holding grid is a rather simple and widely utilized technique for creating micropatterned surfaces. The surface oxidation of a Sylgard 184 film due to UVO exposure is associated with densification and the formation of a silica-like surface layer, which under a TEM grid happens only over the exposed areas of the film, resulting in a physicochemical pattern. It is known that the depth (hD) of the features depends on the duration of UVO exposure (tE). In this article, we show for the first time that hD also depends on the initial film thickness (hF) and the cross-linker percentage (CL, ratio of part A to part B) in a Sylgard 184 thin film. We show that for a specific tE, hD progressively decreases with the reduction in hF. On the other hand, hD shows a nonmonotonic dependence with CL, resulting in patterns with maximum depth for CL ≈ 10.0%. We attribute this observation to the combined effect of resistance against the penetration of the propagation front by the rigid substrate as well as stress relaxation within the exposed parts of the film below the propagating front in films with higher CL values leading to the variation of hD. The observation reported here would allow the potential fabrication of polymer films with physicochemical patterns with feature height on demand by a one-step, facile technique.

Development of a 3-Electrode Setup for the Operando Detection of Parasitic Side Reactions: Exemplified at the Quantification of Released Oxygen

The most considerable push to higher energy density Li-ion batteries (LiBs) has been achieved by incremental improvements of the positive electrode cathode active materials (CAM).1 One approach has been to increase the nickel content of layered transition metal oxide CAMs like lithium nickel cobalt aluminum oxide (NCA; LiNixCoyAlzO2, with x+y+z=1) to above 80%, which has already been achieved on a commercial level. While this increase is accommodated by a higher achievable discharge capacity at a given upper cut-off potential, it also reduces the structural stability of the material at high degrees of delithiation (i.e. at high state-of-charge (SOC)).2,3 The structural instability of the CAM is associated with a release of lattice oxygen at high SOC, starting at approximately 80% SOC.2,3 The release of reactive oxygen species is reported to cause a cascade of degradation mechanisms resulting in capacity fade. During this process, the near-surface region of layered transition metal oxide particles is converted into an electrochemically inactive rock-salt phase, which results in the formation of a resistive surface layer.4 Furthermore, the released oxygen can stimulate the chemical oxidation of the typically employed electrolyte solvents, such as ethylene carbonate (EC), resulting in the formation of CO, CO2, and H2O, which in turn hydrolyzes the electrolyte salt.2,5 Consequently, the detection and quantification of released oxygen for different CAMs and cycling conditions is of high interest. Gas quantification methods such as differential electrochemical mass spectrometry (DEMS) and on-line electrochemical mass spectrometry (OEMS) are powerful tools for the qualitative and quantitative measurement of gaseous species such as O2 and CO2.2,6 However, such methods require an expensive mass spectrometer setup and a sophisticated interface between the LiB cell hardware and the mass spectrometer.Thus, in this study, we will present a simplified method that can detect and quantify released oxygen. The method is based on a setup consisting of a dual working electrode (WE) configuration, namely a primary WE with an NCA CAM (LiNi0.80Co0.15Al0.05O2, from BASF TODA Battery Materials LLC, Japan) and an auxiliary WE with only carbon (Vulcan-type carbon, XC-72, Tanaka, Japan), both being coated with a ; a lithium iron phosphate (LFP) electrode coated on aluminum serves as counter electrode (CE). The latter is delithiated to a degree of 90% and capacitively oversized, allowing the NCA working electrode to be cycled against a constant potential (with the LFP potential being at ~3.43 V vs. Li+/Li).8 While charging the NCA working electrode within the desired potential window, the carbon electrode is polarized to a constant potential of 1.21 V vs. the LFP counter electrode corresponding to ~2.20 V vs. Li+/Li. Since oxygen is reduced at that potential, a reductive current is detected once lattice oxygen is being evolved.9 By the precise knowledge of the number of electrons involved in the reduction of oxygen at the carbon electrode, we are able to convert the reductive current into an amount of released oxygen (e.g., in units of moles of oxygen per gram of cathode active material).We apply the developed cell setup to study the oxygen release characteristics of the NCA when being charged to 5.0 V vs. Li+/Li at 0.1 C and 25 °C, and compare these data to the gassing profile analyzed via OEMS. As will be shown, there is a good agreement between integrated and converted reductive current and the amount of detected O2 in the OEMS.

Impact of Iron Oxide Phases on the Magnetic Induction Heating Capacity of Mesoporous 45SiO2-16.5CaO-24.5Na2O-6P2O5-8Fe3O4 Glass-Ceramics.

Sol-gel-based mesoporous 45SiO2-16.5CaO-24.5Na2O-6P2O5-8Fe3O4 bioglass-ceramics were obtained by substituting magnetite nanoparticles for CaO in a 45SiO2-24.5CaO-24.5Na2O-6P2O5 bioglass composition. To enhance the dissolution of the precursors and to vary the crystalline phases, the as-synthesized ceramic powders were processed for 1 h each at temperatures (TA) between 550 and 700 °C. A gradual decline in the saturation magnetization with an increase in TA was observed, which is linked to the gradual conversion of magnetite into hematite at different TA > 550 °C. All of the processed samples indicated a hydroxyapatite surface layer formation in in vitro tests. Aqueous solutions of the ceramic processed at 600 °C exhibited superior magnetic induction capacity. Thus, the substitution of magnetite nanoparticles for CaO in the base composition, coupled with appropriate heat treatment, results in a promising bioactive glass-ceramic for magnetic hyperthermia treatment of deep-rooted cancer cells.

Colloidal deposits from evaporating sessile droplets: Coffee ring versus surface capture

Suppression of the coffee ring effect is desirable in many industrial applications which utilize colloidal deposition from an evaporating liquid. Here we focus on the role of particle arrest at the liquid-air interface (surface capture) which occurs at high evaporation rates. It is known experimentally that this phenomenon inhibits particles from reaching the contact line, leading to a deposit which is closer to uniform. We are able to describe this effect using a simple 1D modeling framework and, utilizing asymptotic theory, parametrize our model by the ratio of the vertical advection and diffusion timescales. We show that our model is consistent with existing frameworks for small values of this parameter, but also predicts the surface layer formation seen experimentally at high evaporation rates. The formation of a surface layer leads to a deposit morphology which mimics the evaporative flux density and so is closest to uniform when evaporation has a constant strength across the liquid-air interface. Published by the American Physical Society 2024

Biological Surface Layer Formation on Bioceramic Particles for Protein Adsorption.

In the biomedical fields of bone regenerative therapy, the immobilization of proteins on the bioceramic particles to maintain their highly ordered structures is significantly important. In this review, we comprehensively discussed the importance of the specific surface layer, which can be called "non-apatitic layer", affecting the immobilization of proteins on particles such as hydroxyapatite and amorphous silica. It was suggested that the water molecules and ions contained in the non-apatitic layer can determine and control the protein immobilization states. In amorphous silica particles, the direct interactions between proteins and silanol groups make it difficult to immobilize the proteins and maintain their highly ordered structures. Thus, the importance of the formation of a surface layer consisting of water molecules and ions (i.e., a non-apatitic layer) on the particle surfaces for immobilizing proteins and maintaining their highly ordered structures was suggested and described. In particular, chlorine-containing amorphous silica particles were also described, which can effectively form the surface layer of protein immobilization carriers. The design of the bio-interactive and bio-compatible surfaces for protein immobilization while maintaining the highly ordered structures will improve cell adhesion and tissue formation, thereby contributing to the construction of social infrastructures to support super-aged society.

Increasing effect of biocrusts on evaporation is evidenced by simulating evaporation and diffusion experiments and water stable isotope analysis

Evaporation, one of the main components of the water and energy balance between soil and atmosphere, plays a key role in hydrological processes particularly in semi-arid and arid climate regions. As critical living organism communities inhabiting the soil-atmosphere boundary, biocrusts are capable of modifying near-surface soil properties and structure in drylands. However, the roles of biocrusts in mediating soil evaporation still remain greatly controversial, and the literature yet lacks in a systematic assessment. In this study, evaporation experiments were conducted under simulated isothermal and non-isothermal conditions for bare soil and three types of biocrusts (cyanobacterial, moss, and their mixture) sampled from a semi-arid climate region of the Chinese Loess Plateau. During the evaporation, soil temperature and moisture were measured at depths 2, 5, 10, and 15 cm for those biocrusts and bare soil. Their water vapor diffusion process and stable isotopic composition were also analyzed in the laboratory. We found that the measured evaporation yielded 4.9%, 17.5%, and 31.6% higher average evaporation rate for cyanobacterial, cyano-moss, and moss crusts, respectively, when compared to the bare soil. In comparison to bare soil, all types of biocrusts markedly reduced the rate of temperature rise, prolonged the duration of wetting time, and delayed the formation of dry surface layer. The largest regulating effects on soil temperature and moisture were found in the moss crusts instead of cyanobacterial or cyano-moss crusts. The increasing evaporation in biocrusts was attributed to their higher fine particle content, lower bulk density, and greater water holding capacity. Moreover, the water vapor diffusion rate and diffusivity of biocrusts were 18.2% and 16.4% higher than those of bare soil, respectively, which is attributable to the increased total porosity and better soil structure. Additionally, the isotopic composition of soil water (0–50 cm) in bare soil and moss crusts was distributed below the local meteoric water line. The mean δ18O and δ2H in soil water gradually decreased with increasing soil depth, and the moss crusts were more isotopically enriched than bare soil. Based on the enhanced soil evaporation rate, improved vapor diffusivity, and enriched isotopic composition of biocrusts in contrast to bare soil, we conclude that biocrusts exacerbate vapor transport and evaporative loss, and consequently they are crucial surface cover in rebalancing surface ecohydrological and biochemical processes in global drylands. These findings improve our understanding of the complexity of dryland hydrology, and a full consideration should be given in future biocrust studies.

Effect of Europium and Gadolinium Alloying Elements on the Tribological Response of Low Hydrogen Content Amorphous Carbon.

Dopants and alloying elements are commonly introduced in amorphous carbon (a-C) materials to tailor their mechanical and tribological properties. While most published studies have focused on doping and alloying a-C coatings with metals or metalloids, doping a-C films with rare-earth elements has only recently been explored. Notably, our understanding of the shear-induced structural changes occurring in rare-earth-element-containing a-C films is still elusive, even in the absence of any liquid lubricants. Here, the friction response of Eu- and Gd-containing a-C films with low hydrogen content deposited by HiPIMS on silicon was evaluated in open air and at room temperature. The load-dependent friction measurements indicated that the introduction of Gd ((2.3 ± 0.1) at.%) and Eu ((2.4 ± 0.1) at.%) into the a-C matrix results in a significant reduction of the shear strength of the sliding interfaces ((41 ± 2) MPa for a-C, (16 ± 1) MPa for a-C:Gd2.3at.%, and (11 ± 2) MPa for a-C:Eu2.4at.%). NEXAFS spectromicroscopy experiments provided evidence that no stress-assisted sp3-to-sp2 rehybridization of carbon atoms was induced by the sliding process in the near-surface region of undoped a-C, while the amount of sp2-bonded carbon progressively increased in a-C:Gd2.3at.% and a-C:Eu2.4at.% upon increasing the applied normal load in tribological tests. The formation of an sp2-bonded carbon-rich surface layer in a-C:Gd2.3at.% and a-C:Eu2.4at.% films was not only proposed to be the origin for the reduced duration of the running-in period in tribological test, but was also postulated to induce shear localization within the sp2-carbon-rich layer and transfer film formation on the countersurface, thus decreasing the interfacial shear strength. These findings open the path for the use of Gd- and Eu-containing a-C even under critical conditions for nearly hydrogen-free a-C films (i.e., humid air).

Ingenious Architecture and Coloration Generation in Enamel of Rodent Teeth.

Teeth exemplify architectures comprising an interplay of inorganic and organic constituents, resulting in sophisticated natural composites. Rodents (Rodentia) showcase extraordinary adaptations, with their continuously growing incisors surpassing human teeth in functional and structural optimizations. In this study, employing state-of-the-art direct atomic-scale imaging and nanoscale spectroscopies, we present compelling evidence that the release of material from ameloblasts and the subsequent formation of iron-rich enamel and surface layers in the constantly growing incisors of rodents are complex orchestrated processes, intricately regulated and independent of environmental factors. The synergistic fusion of three-dimensional tomography and imaging techniques of etched rodent́s enamel unveils a direct correlation between the presence of pockets infused with ferrihydrite-like material and the acid resistant properties exhibited by the iron-rich enamel, fortifying it as an efficient protective shield. Moreover, observations using optical microscopy shed light on the role of iron-rich enamel as a microstructural element that acts as a path for color transmission, although the native color remains indistinguishable from that of regular enamel, challenging the prevailing paradigms. The redefinition of "pigmented enamel" to encompass ferrihydrite-like infusion in rodent incisors reshapes our perception of incisor microstructure and color generation. The functional significance of acid-resistant iron-rich enamel and the understanding of the underlying coloration mechanism in rodent incisors have far-reaching implications for human health, development of potentially groundbreaking dental materials, and restorative dentistry. These findings enable the creation of an entirely different class of dental biomaterials with enhanced properties, inspired by the ingenious designs found in nature.

Deformation of layered soil

One of the consequences of the aggression of the russian federation in Ukraine is a change in the properties of the surface layers of some regions of the soil. Construction of structures in such areas must be carried out considering the above. In order to create prerequisites for taking into account the artificially created layering of the soil, an algorithm for analytical determination of the stress-strain state of a two-layered soil was developed in a linear setting within the limits of plane deformation. Layers are considered as linear elastic bodies of limited dimensions in the plan. The algorithm is based on the Ery stress function with arbitrary coefficients, on the dependence of the indicators of the stress-strain state of the soil layers on it and on the mechanical indicators of the material of the layers, the thickness of the artificially formed surface layer. The algorithm provides for the formulation of the load conditions by the normally distributed force of part of the soil surface, the conditions of the interaction of the layers, and the unlimited thickness of the main soil layer.The listed conditions and features of the layers constitute a system of linear algebraic equations. The solution of the system of levels provides an opportunity to determine the coefficients of the stress function and, accordingly, to determine the indicators of the stress-strain state of the two-layer soil support. The generalization of the results, carried out by planning the experiment for the selected limits of possible realizations of the mechanical properties of the soil layers, allows for determining the deflections of the surfaces of the layers depending on individual factors.The following is established. The characteristics of the dependences of the deflections of the layer surfaces on other parameters are similar. Maximum deflections decrease with increasing surface layer thickness. Deflections of the interaction surface of the soil layers are linearly dependent on the Poisson ratio of the main soil layer and decrease as the ratio increases. The results obtained within the limits of the linear formulation can be considered sufficiently reliable because they are obtained analytically and generalized by the methods of the linear theory of elasticity and the method of planning the experiment.

Повышение износостойкости цилиндрических поверхностей трения комбинированной электромеханической обработкой

Processing technology and technological equipment for the formation of a wear-resistant surface layer by implanting materials based on tungsten carbide (WC), are viewed. The effect of implanted WC powder on the formation of gradient wear-resistant structures in the friction surface of carbon steel formed during the implementation of combined electromechanical processing (WRCEMP) technology, has been studied. Resulting from heat and pressure impact in the zone of plastic deformation, intensive austenization of steel occurs with dissolution of WC powder and subsequent formation of highly dispersed composite structures caused by the decomposition of undercooled tangstem-supersaturated austenite. Combined comparative friction and wear tests were carried out for structural steel 45 with a graded structure of a hardened surface and rather expensive and technologically- difficult to obtain modern wear-resistant coatings and materials. The issue of WRCEMP technology practical application used for the «axis of satellite – satellite» friction pair is viewed. An assessment of the durability increase of the «axis of satellite – satellite» interface during the implementation of the considered processing methods and innovative technology was taken. Recommendations for the use of combined electromechanical processing technology at machine-building enterprises as a highly effective way to ensure and improve the performance of machine parts at the stage of their manufacture are given.