Surface Layer Of Products Research Articles

Organismal trade‐offs and the pace of planktonic life

ABSTRACTNo one is perfect, and organisms that perform well in some habitat or with respect to some tasks, do so at the cost of performance in others: there are inescapable trade‐offs. Organismal trade‐offs govern the structure and function of ecosystems and attempts to demonstrate and quantify trade‐offs have therefore been an important goal for ecologists. In addition, trade‐offs are a key component in trait‐based ecosystem models. Here, I synthesise evidence of trade‐offs in plankton organisms, from bacteria to zooplankton, and show how a slow–fast gradient in life histories emerges. I focus on trade‐offs related to the main components of an organism's Darwinian fitness, that is resource acquisition, survival, and propagation. All consumers need to balance the need to eat without being eaten, and diurnal vertical migration, where zooplankton hide at depth during the day to avoid visual predators but at the cost of missed feeding opportunities in the productive surface layer, is probably the best documented result of this trade‐off. However, there are many other more subtle but equally important behaviours that similarly are the result of an optimisation of these trade‐offs. Most plankton groups have also developed more explicit defence mechanisms, such as toxin production or evasive behaviours that are harnessed in the presence of their predators; the costs of these have often proved difficult to quantify or even demonstrate, partly because they only materialise under natural conditions. Finally, all multicellular organisms must allocate time and resources among growth, reproduction, and maintenance (e.g. protein turnover and DNA repair), and mate finding may compromise both survival and feeding. The combined effects of all these trade‐offs is the emergence of a slow–fast gradient in the pace‐of‐life, likely the most fundamental principle for the organisation of organismal life histories. This crystallisation of trade‐offs may offer a path to further simplification of trait‐based models of marine ecosystems.

Shot Peening Effect on Sliding Wear in 0.9% NaCl of Additively Manufactured 17-4PH Steel.

The growing demand for modern steels showing corrosion and tribological resistance has led to their increased use in the production of medical devices. This study analyzed the effect of shot peening on wear resistance in 0.9% NaCl solution of 17-4PH steel produced by direct laser metal sintering (DMLS) technology. The study's novelty relies on revealing the effect of shot peening (SP) surface treatment on the wet sliding wear resistance of 17-4PH steel produced with DMLS. Moreover, in the context of 17-4PH steel application for medical devices, the 0.9% NaCl tribological environment were selected, and SP processes were conducted using steel CrNi shot and ceramic (ZrO2) beads. The up-to-date scientific literature has not identified these gaps in the research. DMLS technology makes it possible to obtain products with complex architectures, but it also faces various challenges, including imperfections in the surface layer of products due to the use of 3D printing technology itself. The chemical and phase composition of the materials obtained, Vickers hardness, surface roughness, and microscopic and SEM imaging were investigated. Tribological tests were carried out using the ball-on-disc method, and the surfaces that showed traces of abrasion to identify wear mechanisms were subjected to SEM analysis. The XRD phase analysis indicates that austenite and martensite were found in the post-production state, while a higher martensitic phase content was found in peened samples due to phase transformations. The surface hardness of the peened samples increased by more than double, and the post-treatment roughness increased by 12.8% after peening CrNi steels and decreased by 7.8% after peening ZrO2 relative to the reference surfaces. Roughness has an identifiable effect on sliding wear resistance. Higher roughness promotes material loss. After the SP process, the coefficient of friction increased by 15.5% and 20.7%, while the wear factor (K) decreased by 25.9% and 32.7% for the samples peened with CrNi steels and ZrO2, respectively. Abrasive and adhesive mechanisms were dominant, featured with slight fatigue. The investigation showed a positive effect of SP on the tribological properties of DMSL 17-4PH.

Электроискровое модифицирование поверхности аддитивного сплава ВТ6 высокоэнтропийным и аморфным электродами

Unsatisfactory quality of the surface layer of additive products, in particular increased surface roughness, prevents the widespread use of electron beam powder bed fusion (EBPBF). Electrospark treatment (EST) is one of the methods for smoothing and hardening the surface layer. The work shows the possibility of modifying the surface of additive VT6 alloy samples by reactive EST with multicomponent electrodes. For this purpose, the authors used electrodes made of the Fe48Cr15Mo14Y2C15B6 bulk metallic glass forming alloy and the FeCoCrNi2 high-entropy alloy. Based on the results of scanning electron microscopy, it was identified that after EST, both modified layers have a thickness of about 16 μm. X-ray diffraction phase analysis showed that in the case of treatment with an amorphous electrode they contain carboborides of the Ti(B,C) type, and in the case of treatment with a high-entropy electrode – intermetallic of the Ti2(Fe,Ni) type. The modified layers have average hardness values of 19 and 10 GPa and elastic modulus of 234 and 157 GPa, respectively, which significantly exceeds the values of these parameters for the EBPBF-grown VT6 alloy. Electric discharge modification of the surface with multicomponent electrodes led to a decrease in roughness by 8...11 times due to the melting of the protrusions and filling of the dimples with the melt to a depth of more than 50 μm. A comparative analysis of the results of tribological tests showed a change in the wear mechanism as a result of EST of the additive VT6 alloy. Wear resistance increased by 4 and 3 orders of magnitude when using electrodes made of a bulk metallic glass and high-entropy alloy, respectively.

The Role of Carbides in Forming the Steels Structure and Properties under Pulsed Laser Irradiation

Introduction. At present, in scientific publications, there is no unambiguous understanding and reasoned metal physical justification of the role of the carbide phase of irradiated materials in forming the required structure and achieving a given degree of hardening of surface layers of steels during pulsed laser treatment, especially in the zone of laser hardening from a solid (austenitic) state. The solution to this issue is of great importance, since it allows us to reasonably and purposefully design the required structure of surface layers of products of various functional purposes with high performance properties. The complexity and insufficiently detailed study of the process of structure formation in the surface layers of steels under extreme thermal effects of pulsed laser radiation required a series of metal physical experiments to study the fine structure of steels after high-speed high-temperature hardening. The aim of this article was to obtain, quantify and critically analyze the array of results of metal physical studies and to assess the degree of influence of the carbide phase on the formation of structure and properties of surface layers of steels in the process of pulsed laser hardening in different modes, that is, with and without melting the surface of the samples. Materials and Methods. In the work, carbon and alloyed tool steels were subjected to surface laser irradiation at a Kvant 16 installation. The radiation power density was 70–200 MW/m2. Optical, scanning probe and electron microscopy were used in conducting metal physical studies, as well as methods of diffractometric, spectral and durometric analysis of steels before and after laser treatment. Results. It was shown that laser treatment of steels with a radiation power density of 130–200 MW/m2 led to a local change in the chemical composition in the laser-fused areas of the spot, partial or complete dissolution of carbides present in the irradiated metal and an increase in the amount of residual austenite in the fused areas up to 40–60 %. It was found that on P6M5 steel, the maximum possible hardness of the irradiated zones was achieved by dissolving 30 % of carbides, on 9XC, HVG steels — 60–70 %. It was shown that under pulsed laser irradiation with q=70–125 MW/m2, that is, without melting the steel surface, "white zones" formed around carbide inclusions under the influence of thermo-deformation stresses at the boundaries of the "carbide – steel matrix" composition. They had irretrievability, dispersion of the structure and increased hardness (10–12 GPa). It was determined that the maximum hardness of laser-hardened metal in the zones of laser hardening from a solid state was achieved if the "white zones" occupied 40 % of the irradiated area of steel. It was found that the dispersion of carbides in this case was 0.5–1.5 microns. Discussion and Conclusion. The results of the conducted studies indicate that in order to obtain the best combination of hardness and viscosity of the irradiated zones during laser treatment with melting of the surface of steels of different chemical composition, it is necessary to dissolve different amounts of carbides. The dispersed structure of laser-fused steel zones, along with a sufficiently high content of residual austenite, predetermine the possibility of improving the operational characteristics of irradiated materials, especially under conditions of external shock loads. The analysis of the conducted metal physical studies irradiated without melting the surface of steels allows us to conclude that in order to obtain a high degree of hardening, it is necessary and expedient to ensure the presence of a certain volume of dispersed carbides in the structure of the irradiated steel. The structural composition of "white zones" formed during laser treatment without melting the steel surface contributes to obtaining a unique level of operational properties. The results of the performed studies contribute to the theory of steel structure formation under conditions of extreme heat exposure and allow for a rational choice of modes of surface laser processing of products and their operability.

Particulate organic carbon export fluxes estimates by 234Th[sbnd]238U disequilibrium in the oxygen minimum zone off the Peruvian coast

The Peruvian upwelling zone is one of the most productive marine ecosystems in the world with a spectacular, pronounced oxygen minimum zone (OMZ). Globally OMZs are increasing in size and intensity with far-reaching consequences for the marine biological carbon pump and carbon export; thus, these zones need to be carefully monitored to be able to understand future climate change impacts. The current study was carried out in 2013 and 2017 to quantify the vertical flux of organic matter exported out of the productive surface layer by measuring 234Th238U disequilibria in the water column. Samples were collected in January 2013 and May 2017 along an identical transect located at 12°S off the Peruvian coast near Lima, Peru. Th-234 fluxes ranged from 0 to 2088 ± 95 dpm m−2 d−1 in 2013 and 698 ± 63 to 3648 ± 113 dpm m−2 d−1 in 2017. The corresponding POC fluxes varied between 0 and 164.2 ± 7.9 mg C m−2 d−1 in 2013 and 22.7 ± 2.7 to 133.1 ± 15.2 mg C m−2 d−1 in 2017, with POC fluxes gradually decreasing with distance from the coast. Despite higher POC fluxes, the export efficiencies were found to be extremely low due to high particle remineralization rates observed within the euphotic zone.

Amazon River plume habitats shape planktonic cnidarian assemblages in the Western Atlantic.

The impact of the Amazon River freshwater plume on planktonic cnidarians over neritic and oceanic provinces is unknown. To provide further knowledge we took advantage of an oceanographic cruise performed in October 2012 in the Western Atlantic off the North Brazilian coast (8°N, 51°W-3.5°S, 37°W). A complex and dynamic system was observed, with strong currents and eddies dispersing the plume over a large area. Our results show that the Amazon River shapes marine habitats with a thin highly productive surface layer compressed by a deeper oxygen minimum zone both over the shelf and in the open ocean. We hypothesized that such habitat structure is particularly advantageous to planktonic cnidarians, which have low metabolic rates, being able to survive in hypoxic zones, resulting in high species richness and abundance. Over the shelf, distinctions were sharp and the area under the influence of the plume presented a diverse assemblage occurring in large abundance, while outside the plume, the hydromedusa Liriope tetraphylla was dominant and occurred almost alone. Divergences in the oceanic province were less pronounced, but still expressive being mostly related to the abundance of dominant species. We concluded that Amazon River plume is a paramount physical feature that profoundly affects the dynamics of the mesoscale habitat structure in the Western Equatorial Atlantic Ocean and that such habitat structure is responsible for shaping planktonic cnidarian assemblages both in neritic and oceanic provinces.

THERMODYNAMIC MODELING OF OBTAINING WEAR-RESISTANT COATINGS USING COMPOSITE POWDER CHARGES

Abstract. The article provides an overview and analysis of obtaining wear-resistant coatings for parts working in aggressive environments of metallurgical production. The solution of these problems is associated with the hardening of the surface layers of products. Their role in the durability of machines and mechanisms has especially increased at the present time, since the development of most industries is associated with an increase in loads, temperatures, and the aggressiveness of the environments in which the part operates. The titanizing process is an effective method of increasing the reliability and durability of machine parts, tools and technological equipment due to the creation of titanized layers on the surface of the machined parts, which have a unique set of physical and chemical properties. The results of thermodynamic modeling for the production of wear-resistant titanium-based coatings for the determination of rational composite powder charges are presented. The use of thermodynamic modeling makes it possible to quantitatively model and predict the composition and properties of complex heterogeneous, multi-element, multi-phase systems in a wide range of temperatures and pressures, considering chemical and phase transformations. The results of research on wear resistance revealed that, when tested under friction-sliding conditions, the best wear resistance among the considered alloyed titanium coatings was achieved by coatings alloyed with chromium and silicon. Their wear resistance is 1.7-1.9 times higher than that of coatings obtained under isothermal conditions.

Comprehensive Estimation of Changes in the Microgeometry of Steel 45 by Ultrasonic Plastic Deformation with a Free Deforming Element

A method of ultrasonic surface plastic deformation is widely used to change the properties of the surface layers of metal products. Under the influence of this type of treatment, the structure of the material changes, microhardness increases, roughness decreases, internal tensile stresses are removed, and compressive stresses are created. Now many types of ultrasonic surface plastic deformation have been developed, which differ in the degree of impact on the material. The object of this paper is to study the change in the microgeometry of steel 45 (ASTM M1044; DIN C45; GB 45) under the action of ultrasonic plastic deformation by a free deforming element (indenter in the form of a surface rolling ball). During the study, factors that have the greatest influence on the change in the microgeometry of the sample during treatment were identified. These include the initial roughness of the sample, the number of passes of the indenter, the feed of the indenter, the force with which the indenter is pressed to the treated surface, and the amplitude of the oscillations of the ultrasonic horn. The paper presents the dependences of changes in the main roughness parameters on the above factors. The value of the initial roughness at which it is possible to obtain a uniform surface microrelief is determined. The optimization of treatment parameters providing a change in the height and step parameters of roughness was carried out. Recommendations for choosing the most effective technological modes of ultrasonic treatment of steel 45 with a surface rolling ball are given.

Possibilities of Using of Surface and Subsurface Waves’ Amplitude-Angle Characteristics for Control of Materials with Surface-Hardened Inhomogeneous Layer

Improving the efficiency of ultrasonic control of hardened surface layers of metal products with a heterogeneous structure obtained using different technologies is a pressing problem of industrial production. The purpose of this work was to investigate the possibilities of measuring the depth of the surface inhomogeneous layer of steel objects on the basis of the use of amplitude and amplitude-angle characteristics of surface and subsurface transverse waves.The analysis of ultrasonic methods of control of physical and mechanical properties of metals by using surface and subsurface waves and experimentally investigated amplitude-angular characteristics of surface waves, the maximum angle of which increases by 3° at change of dimensionless layer depth hλ from zero to0.82. For the first time, the ratio of normalized amplitudes of surface waves taken at certain angles on theamplitude-angle characteristic curve obtained in the echo mode was proposed to be used as correlating parameters with the depth of the hardened layer. As a result of this research, the possibility of using a phased array transducers to solve the above problems.The effect of the hardened layer depth varying from zero to five in the working frequency range of 1.8– 10 MHz on the peculiarities of the refraction effect (including interference) and dependence of the subsurface wave amplitude on the acoustic base has been studied, making it possible to establish conditions that provide for the determination of the hardened layer depth.Circuit solutions have been offered in order to increase the efficiency of control of properties of the surface layers of metal articles on the basis of utilization of small-aperture transducers and ultrasonic reflectors making it possible to form fields of surface waves of different directional pattern.

Effect of Air Storage on Stress Corrosion Cracking of ZK60 Alloy Induced by Preliminary Immersion in NaCl-Based Corrosion Solution.

The preliminary exposure of Mg alloys to corrosion solutions can cause their embrittlement. The phenomenon is referred to as pre-exposure stress corrosion cracking (PESCC). It has been reported that relatively long storage in air after pre-exposure to the corrosion solution is capable of eliminating PESCC. This effect was attributed to the egress of diffusible hydrogen that accumulated in the metal during pre-exposure. However, recent findings challenged this viewpoint and suggested that the corrosion solution retained within the side surface layer of corrosion products could be responsible for PESCC. The present study is aimed at the clarification of the role of hydrogen and the corrosion solution sealed within the corrosion products in the "healing" effect caused by post-exposure storage in air. Using the slow strain rate tensile (SSRT) testing in air and detailed fractographic analysis of the ZK60 specimens subjected to the liquid corrosion followed by storage in air, we found that PESCC was gradually reduced and finally suppressed with the increasing time and temperature of air storage. The complete elimination of PESCC accompanied by recovery of elongation to failure from 20% to 38% was achieved after 24 h of air storage at 150-200 °C. It is established that the characteristic PESCC zone on the fracture surface is composed of two regions, of which the first is always covered by the crust of corrosion products, whereas the second one is free of corrosion products and is characterised by quasi-brittle morphology. It is argued that the corrosion solution and hydrogen stored within the corrosion product layer are responsible for the formation of these two zones, respectively.

Analysis of Li Dissolution/Deposition Behavior in LiNO3 Electrolytic Solution for Li-Air Battery

Li-air batteries (LAB) have been attracting much attention because of their theoretical energy density of 3500 Wh kg−1, which is five times as high as that of Li-ion batteries. However, many problems remain to be challenged in every component of the battery: air electrodes, electrolytic solutions, Li electrodes, etc. As for the Li electrode, we have reported some results on the reversibility of the Li dissolution/deposition reaction by using Li | Li symmetric cells with tetraglyme (G4) -based electrolytic solution [1, 2]. In particular, it has been confirmed that in the 1.0 M LiNO3/G4 electrolyte under an O2 atmosphere, a Li2O protective layer is efficiently formed on the Li electrode at a current density of 0.4 mA cm-2, and Li dendrite formation is suppressed. In this study, we expanded test conditions in current densities up to 2.0 mA cm-2 and temperatures at 10 °C to 50 °C to reveal whole picture of dissolution/deposition behavior of the Li electrode.A Li | Li symmetric cell was assembled using a pair of Li foils inserted by a separator (Celgard 2400) and 1.0 M LiNO3/G4 or 1.0 M LiTFSI / G4 as the electrolytic solutions in an Ar-filled glove box. The Li dissolution/deposition cycle tests by the cells were carried out at 10, 30 and 50℃ at a constant current density between 0.2 to 2.0 mA cm-2 regulated by a constant capacity of 0.5 mAh cm− 2. After the tests, the Li electrodes were taken out of the cells followed by rinsing in G4 in the glove box, the surfaces of which were observed by SEM and analyzed by XPS. Figure 1 showed Li | Li cell test results at 0.4 mA cm−2 and 30 ℃ in different electrolytic solutions. Fig ure 1a for that in 1.0 M LiTFSI/G4 showed gradual decrease in overvoltages and unstable polarization curves. These two features suggested that the Li electrode protection by the Li2O layer from O2 gas could not withstand the current density and the exposed Li metal reacted with the solvent and electrolyte, resulting in growing Li dendrite deposition. On the other hand, Figure 1B for that in the 1.0 M LiNO3 / G4 overvoltages, suggesting suppressed Li-electrolytic solution showed very flat polarization plateaus and slightly growing dendrite formation. The difference between Figure 1a and 1b demonstrated the effect of Li2O protective layer of Li surface formed by the reaction between Li and NO3 −. Figure 2 showed the SEM image of the Li electrode after the dissolution/deposition test for 15 cycles and the surface analysis by C1s XPS. Figure 2a for LiTFSI/G4 electrolytic solution showed bulky surface layer as thick as 30 µm accompanied by a large dent. Figure 2b suggested various kind of C-containing deposits on the Li surface, which was presumably decomposed products of electrolytic solution. Therefore, Figure 2a and 2b were well consistent with Figure 1a which suggested successive surface reactions. Figure 2c and 2d for LiNO3/G4 electrolytic solution, on the contrary, showed thin surface layer and poor amount of surface products, even though the current density, 0.6 mA cm−2, was higher than that in Figure 2a, 0.4 mA cm−2. These results suggested steady surface protected by Li2O layer and were also consistent with Figure 1b.Other results presenting the effect of current densities and temperatures will be reported in our presentation to clarify the whole picture of Li dissolution/deposition reaction mechanism.

The effect of pressure in the working chamber of a processing unit on the quality indicators of the composite structure formed in the metal product surface layer at low-temperature plasma modification

The paper proposes an approach to increasing the efficiency of plasma modification of the metal product surface layer based on the study of the effect of pressure in the working chamber of a technological unit on its course and outcomes. It was found that there is such influence, and it is manifested in a heat flow direction change and leads to the intensification of either heat conduction (with increasing pressure), or heat transfer and radiation from the surface (with decreasing pressure). In the first case this leads to the formation of the most compacted composite structure in the surface layer, and to the transition layer formation between the structure and the main material of the product. In the second case the compaction of the surface layer is minimal, no transition layer is formed. The pressure change effect mechanism associated with the violation of the dynamic equilibrium between adsorbed and desorbed particles on the product surface when changing the temperature regime has been identified. It is shown that after switching off the plasma, it is necessary to control the heat flow propagation, and that the course of the lag temperature curve can serve as an operational indicator of the control quality.

Dissolved organic carbon and nitrogen cycling along the west Antarctic Peninsula during summer

The cycling of dissolved organic matter in the productive west Antarctic Peninsula (WAP) region is not well understood. For this study, dissolved organic carbon (DOC) and nitrogen (DON) concentrations and other biogeochemical measurements were collected along the WAP shelf during austral summer 2017. Concentrations of both DOC and DON in the upper ocean were lower than in lower latitudes (38.13–48.00 μmol C L−1, 2.90–10.52 μmol N L−1). DOC is produced along with particulate organic carbon during primary production, and is subsequently consumed by bacteria. DON shows high variability and is more likely the product of bacterial activity only in the surface waters. The N-isotopic composition of nitrate and particulate nitrogen showed intense nitrification, especially along the coast, and supports the findings of intense upper ocean cycling of organic matter of both particulate and dissolved forms. Export of DOM from the productive surface layer was negligible in the shelf waters of the WAP. Samples from glacial melt areas showed increased DON concentrations (7.88–10.52 μmol N L−1) so we conclude that increasing warming and continuing melting of Antarctic glaciers may lead to higher concentrations of dissolved organic matter but also higher bacterial activity with more intense upper-ocean carbon and nitrogen cycling.

Creation of promising technologies for producing holes in parts of a high-frequency ion engine

The article considers application areas of various machining methods for perforating holes in parts with unpredictable surface fluctuations. The most effective methods of obtaining holes in parts of a high-frequency ion engine are shown. Studies of perforation technologies using various machining methods have been carried out. Qualitative relations between the geometric dimensions of a spherical billet perforated using a mechanical method, and the quality of the product surface layer are considered. An analysis of modern machining methods is carried out; promising technologies for obtaining holes in parts with a variable profile are presented. The necessity of using high-tech technologies for perforation in high-frequency ion engine parts is justified. The results obtained allow us to significantly expand the production technological capabilities, as well as significantly improve the technical characteristics of special equipment products in mechanical engineering.

Dissolved Trace Metals and Organic Matter Distribution in the Northern Adriatic, an Increasingly Oligotrophic Shallow Sea

We report a monthly distribution of Zn, Cd, Pb, Cu, Ni and Co, biologically relevant trace metals (TMs), within one year, in the productive surface layer at two stations with different trophic characters in the northern Adriatic (NA). The TM data was accompanied by a multivariable dataset, including dissolved organic carbon (DOC), surface-active organic substances (SAS), nitrogen-containing polymeric organic material (N-POM), nutrients, pH, dissolved O2, chlorophyll a (Chl a), seawater temperature, and the Po River discharge rate. At the eu- to mesotrophic station 108, the concentrations of dissolved TMs were 5–116 nM for Zn, 0.04–0.18 nM for Cd, 0.05–0.63 nM for Pb, 3–17 nM for Cu, 4–11 nM for Ni, and 0.2–1.2 nM for Co, while at the oligotrophic station 107, they were 6–224 nM for Zn, 0.03–0.16 nM for Cd, 0.05–1.25 nM for Pb, 3–17 nM for Cu, 4–19 nM for Ni, and 0.1–0.7 nM for Co. The characterization of organic matter (OM) in conjunction with the analysis of correlations with TMs indicated that the OM–TMs interactions differed between the two stations; namely, the freshly produced OM detected at station 108 was probably involved in the complexation of Cu, Co, Cd, and Ni, whereas at station 107, such complexation processes were not present. Accumulation of DOC was observed during the summer months at both stations. Our results present a significant contribution to biogeochemical studies in the NA by focusing on the complexity of TM–OM interactions, which is a prerequisite for interpretation of their responses to local and global changes.

MODELING THE EFFECT OF STOCHASTIC DEFECTS FORMED IN PRODUCTS DURING MACHINING ON THE LOSS OF THEIR FUNCTIONAL DEPENDENCIES

The article investigates the influence of hereditary defects formed in the surface layer of products from metals of heterogeneous structure on the quality of surfaces treated with finishing methods. The research is based on an integrated approach based on the results of the deterministic theory of defect development and methods of probability theory. The treated layer of the product is considered as a medium weakened by random defects that do not interact with each other, namely: structural changes, cracks, inclusions, the parameters of which are random variables with known laws of their probability distribution. The causes of structural changes, crack formation on the treated surface product depending on different types of probability distribution of dimensions are investigated: length, depth of defects, and their orientation. From these positions, technological possibilities of their elimination by definition of branch of combinations of the technological parameters providing necessary quality of the processed surfaces are considered. Modeling of thermomechanical processes in the treated surface containing hereditary defects is carried out based on thermoelastic equations with discontinuous boundary conditions in the places of their accumulation. The research used the apparatus of boundary value problems of mathematical physics equations, the method of singular integral equations for solving problems of fracture mechanics, Fourier-Laplace integral transformations for obtaining exact solutions, the method of constructing discontinuous functions. The dependences determining the intensity of stresses in the vertices of hereditary defects are obtained. A method for predicting the nature of crack formation depending on the probability distribution of defects, the values of heat flux entering the surface layer of the processed product has been developed. It is established that the increase in the homogeneity of the material leads to an increase in the value of heat flux, which corresponds to a fixed probability of failure.

NANOSTRUCTURING WEAR-RESISTANT COATINGS FOR THE WORKING PARTS OF AGRICULTURAL MACHINES BY VIBRATION PLASMA TREATMENT

The use of technologies for hardening the surfaces of machine parts and mechanisms using concentrated energy flows increases the competitiveness of products. The simplest and most accessible of them are plasma technologies for hardening worn surfaces using electric spark and vibration arc discharges. (Research purpose) The research purpose is studying the possibilities of vibrating plasma technologies for hardening the surfaces of metal products for use in the real sector of the economy, the physical and mechanical properties and structural changes of the surface layer of these products. (Materials and methods) Two batches of samples from 65G steel, widely used for working bodies of agricultural machinery, were processed. One batch consisted of three samples: first sample is initial, second sample with electric spark treatment, third sample was subjected to vibration arc treatment with additional hardening by an electric spark. The morphology of the surface and the elemental composition of the samples were studied using a scanning electron microscope EVO 50 XVP from Zeiss. The microstructure was determined using an inverted metallographic microscope Olympus GX51 with magnification from 50 to 1000x. (Results and discussion). Vibrating plasma methods allow nanostructuring of the surface layer of metal products with the introduction of a whole list of alloying elements of carbide materials into the structure of the surface layer of the product, carburization of this layer and the creation of a hardened layer consisting of oxides, carbides, borides and nitrides. In the process of vibrating plasma treatment, a hardened zone of the surface layer with mixed elements of the base and filler material and a zone of thermal influence are formed in the surface layer of the sample. (Conclusions) The surface layer formed during vibrating plasma treatment is a new nanostructured composite structure. The upper thin layer consists of the anode material modified by elements of the cathode material and the interelectrode medium. Under the upper layer there is a modified hardened layer consisting of a mixture of anode and cathode materials.

AFM study of the morphology of elastomers based on polyurethanimides with various rigid and flexible fragments

The morphological characteristics of the surface of a number of films of elastomers based on polyurethanimides (PUI) were studied by atomic force microscopy (AFM). Significant differences in the surface morphology of PUI films were found depending on the composition: from granular morphology with different grain sizes or spongy morphology with nano - and submicron pores and cavities on the surface, to spherulitic morphology. It is shown that the roughness of the free surfaces formed during the films formation from the solution is significantly lower than the roughness of the surface which was in contact with the substrate. The influence of the chemical structure and size of the rigid diamine fragments in PUI macromolecules on the morphology of the film surface and the presence of different phases in the AFM torsion mode is established. The comparison of the deformation and strength characteristics showed high values of the elongation at break (more than 1400%) in the PUI films with a developed porous structure of both surfaces. The results obtained show the need to control and take into account the morphological parameters of the surface layers of products made of highly elastic imide-containing materials for their use for technical and other purposes. Keywords: synthesis of polyurethanimides, atomic-force microscopy, elastomer films morphology, surface roughness, viscosity and strain-strength characteristics.

Разработка пористых титановых имплантатов для межтелового спондилодеза

Relevance Application of 3D printing using the method of selective laser fusion for production of intervertebral cages is a topical trend of the spinal surgery. Purpose Assessment of the efficiency and safety of original interbody fusion implant application made of titanium alloy according to 3D printing technology with selective laser fusion. Materials and methods The original flattened bean-shaped cages, with an integral side part and an internal configuration in the shape of three-dimensional 1.5 × 1.8 mm porous lattice were tested . The products were made of Ti6Al4V powder using 3D printing technology with selective laser fusion. Post-processing of the products surface included abrasive blast cleaning using the SLA method and sterilization with ethylene oxide. Experiments on modeling interbody fusion with replacement of intervertebral discs with cages at levels L4 – L5 and L5 – L6 were performed in 8 mongrels. Additional primary stabilization of the lumbar spine was produced with an external fixator within 30 days after implantation. The total follow-up period lasted 180 days. Radiography, scanning electron microscopy, roentgenospectral and biochemical analysis methods were applied. Results X-ray examination demonstrated the contact between the frontal surfaces of the cages and the bone tissue of the vertebral bodies and the development of fusion in all experimental animals. Biochemical analysis did not reveal the signs of intoxication, indicating the danger of the products application. The microrelief of the implants was characterized by microroughness ranged from 1to 50 μm. In the surface layer of products, in addition to the elements of titanium, aluminum and vanadium, the carbon, oxygen, silicon, trace amounts of other organic and inorganic elements were found. Newly formed bone trabeculae were macroscopically and submicroscopically visualized in the sawcuts of bone blocks in the porous lattice of the internal part of the implants. Conclusions Experimental testing of porous implants made of titanium alloy using selective laser fusion has shown their effectiveness in obtaining interbody fusion and acceptable safety.

Substantiation of the technology for controlling the process of low-temperature plasma modification of metal product surface layer by the electrical signal parameters

Substantiation of the technology for controlling the process of low-temperature plasma modification of metal product surface layer by the electrical signal parameters