The paper presents research on the effect of technological parameters of high-energy processing on the performance properties of powder coatings made of cermet. The use of pulse-plasma treatment is considered as an example of high-energy modification of coatings. As used powder coating materials, various versions of carbide-containing ceramics with the addition of a solid lubricant in an iron-based metal matrix have been selected in the paper. Coatings of carbide-containing ceramics with the addition of a solid lubricant in an iron-based metal matrix on are being developed to replace those of a nickel-based matrix. Such factors as crack resistance, wear resistance, workability, brittleness, as well as economic components often limit the use of powder materials based on carbide ceramics with the addition of solid lubricant in the matrix based on nickel. When only the wear process determines the service life of a part, such powder materials should be replaced with cheaper powder materials based on carbide ceramics with the addition of solid lubricant in an iron-based matrix. The proposed developments increase the wear resistance of the plasma coating due to the introduction of high-chromium steel and molybdenum into the material. Optimum porosity is formed in the initial powder mixture during the synthesis of FeCrMo–MoS₂–TiC composite materials, there is an improvement in the technological parameters of powder materials, their utilization rate in plasma spraying increases, and the technology of applying wear-resistant plasma coatings becomes cheaper. The addition of the Mo element to the FeCr binder increases the wetting of titanium carbides by the binder melt during self-propagating high-temperature synthesis of the developed composite powder. Subsequent layer-by-layer processing of plasma-sprayed coatings from powders of the developed ceramics using repetitive pulses of plasma flows using different energy levels makes it possible to create strictly defined structures with necessary and controlled porosity, which decreases in a certain sequence from the outer treated layers to the base. Such treatment contributes to a significant increase in the wear resistance of the treated friction surfaces, increases the oil holding capacity, in addition, an increased adhesive and cohesive strength of the formed layers bordering the substrate is formed. Processing distances, the total number of impacts have been varied in accordance with the methodological developments, when changing the applied technological characteristics of pulse-plasma effects. The total number of plasma pulses influences on the created thickness of the plasma coating layers after treatment and contributes to the melting  with compaction of the coatings obtained by the plasma treatment and the creation of a structure with hardened characteristics.

 

Abstract. A device design is proposed that makes it possible to obtain composite castings of sliding bearings based on babbitt by mixing alloying additives from antifriction powders of solid lubricants (graphite, molybdenum disulfide, etc.) into the melt, having a density significantly lower than the density of babbitt itself.  The principle of mixing is based on the use of  numerous turbulent flows resulting from the rotation of a gating rod with a wire pile in the melt material, the packing density coefficient of which is not less than 0.1. Due to the suction effect of these flows, non-metallic particles of solid lubricant powder do not float to the surface of the melt and, after crystallization, remain in the body of the casting. The supply of alloying powder of solid lubricant is carried out simultaneously with the supply of  the babbitt melt through the central and distribution gating channels made in a rotating rod. Under the action of centrifugal forces, powder particles and melt material flow through distribution channels to the walls of the mold (mold), passing through the rotation zone of the metal pile. In this case, intensive mixing of the powder particles with the melt material occurs due to the suction effect of turbulent flows arising behind the moving pile. In addition, as a result of the rotation of the wire pile, dendritic constituents are crushed in babbitt castings.  Metallographic studies of the castings obtained on the developed device have shown that the structure of the casting obtained by traditional technology contains large quantities of solid crystals of intermetallic compounds SnSb and Cu₃Sn, while in the structure of the casting obtained using the proposed device, along with the aforementioned intermetallic compounds, particles of solid lubricant C + MoS₂ powder embedded in the crystallized melt are observed.

 

New two-layer wear-resistant coatings of the composite type “thermal diffusion layer – vacuum ion-plasma coating TiAlN” have been obtained, their durometric and tribological properties have been investigated in the paper. The study has made it possible to establish influence of  preliminary  thermochemical  treatment of  a steel substrate on the  formation of  surface thermal diffusion layers is significantly higher than on unhardened steel substrates. Thus, the nano-hardness of TiAlN 1 μm-thickness coatings on substrates with a carbonitride layer when indented to a depth of 0.1–0.9 μm, is 1.9 times higher, the elastic modulus is 1.7 times higher, the ductility index H/E^* is higher by 13.0 %, the rate of elastic recovery H²/E^* and the rate of plastic deformation resistance H³/E^*2 – have been increased by more than 2.1 and 2.4 times, respectively. The fracture toughness has been increased by 4.5 times. Preliminary boriding of the steel substrate leads to an increase in the actually measured nanohardness of the coated surface up to 1.8 times, elastic modulus up to 1.8 times, H³/E^*2 – up to 1.8 times, H³/E^*2 – up to 1.8 times, surface hardness – up to 10.0 %, while maintaining or increasing the plasticity index H/E up to 8.0 % in comparison with the characteristics obtained by nano-indentation of the TiAlN coating on an unhardened steel substrate. The discovered phenomenon is associated with an increase in the contribution of the hardened substrate to the elastic restoration of the coating and the indentation response of the surface. The paper presents the results of practical application of the developed wear-resistant compositions.

The relative actuation of the tool is considered, which makes it possible not to take into account the hard-to-determine technological coefficients depending on external conditions, as well as the physical, mechanical and technological properties of the processed material. This response is determined by the distribution of the relative sliding speeds and pressure in the contact zone of the tool and the work-piece, as well as the processing time, which are characterized by the geometric and kinematic parameters of the machine operating mechanism and processing modes. A phased simulation of the actuation process of the tool working surface is proposed: without oscillation of  the upper link and with its return-rotational  movement. According to this approach, at the first stage, the distribution of the relative sliding speeds and pressure in the contact zone of the grinding surfaces is calculated, and at the second stage, when determining the relative response at the points of the lower link (tool), the movement of these points from the areas of the contact zone with same values of the indicated quantities in the area with others is monitored. A mathematical model of the process of shaping a flat surface under conditions of free grinding of the body and counter-body is obtained, which establishes quantitative relationships between the machining modes and the shape of the treated surface and is a simulation numerical model, since it allows to obtain the distribution of relative triggering over the working surface of the tool for pre-selected time points.

Ultrasonic methods for eliminating vascular obstruction are widespread throughout the world. The advantages of such methods are the absence of surgical intervention, a low probability of complications, and a low cost of treatment. Ultrasonic waveguide systems for the destruction of intravascular formations and elimination of vessel obstruction are made in the form of hollow or continuous long rods of constant and variable cross-section (concentrator waveguides). The development of  new methods of  treatment based on the use of  stepped  ultrasonic  waveguide systems of a tubular type is underway, allowing to supply fluids to the zone of dislocation of an intravascular formation. The presence of a hollow spherical tip with axial and lateral micro-holes in the distal part of such waveguide systems, designed to influence the resulting cavitation jet, both on the intravascular mass and on the affected area of the vascular wall, allows the vessel to be restored with a simultaneous increase in the elasticity of the vascular wall. Such a combined vibration and shock and cavitation effect is currently one of the most effective methods of treating intravascular formations. An analysis of the sizes, structures and materials for the manufacture of tubular concentrator waveguides shows that their shaping can be carried out by various methods: cold deformation, mechanical, hydroabrasive treatment, using welding (or related processes), electrolytic, and also combined processing methods. The existing processes for obtaining long products of small diameter, based on plastic methods, mechanical processing and physical and technical methods, have a number of disadvantages that do not allow the manufacture of tubular concentrator waveguides with the required characteristics. The paper presents the results of the analysis of literary sources, as well as the results of experimental studies, which have made it possible to substantiate the choice of methods for the step-by-step manufacture of tubular concentrator waveguides: obtaining a tubular stepped element by unrestricted drawing, obtaining a working tip by distributing and crimping, obtaining side holes in the working tip by electrochemical сutting.

Light self-destruction-degradation of the second type has been observed in samples of semiconductor lasers with electronic  energy  pumping with high  optical  homogeneity and good quality of surface treatment.  In these  samples,  damage appeared in the form of cords perpendicular to the ends of the resonator. According to the current understanding of the passage of powerful light streams through various media, the emergence of narrow light channels is due to the phenomenon of self-focusing. It refers to the fundamental physical mechanisms of propagation of laser radiation and is caused by nonlinear phenomena arising in a medium under the influence of high-power laser radiation. The physical reason for self-focusing is an increase in the refractive index n in a strong light field. Thermal self-focusing is the most probable cause of radiation redistribution in the active region of the crystal. However, it is possible that in the initial stage of the appearance of light channels a certain role is played by the growth of the intensity of radiation in certain sections of the crystal because of the instability of generation or small fluctuations in the pump current density. Then the process acquires an avalanche character, since the localization of the ray in the channel increases the density of light radiation which can lead to overheating of the substance and the activation of the thermal self-focusing mechanism. The experiments performed in this paper have shown that optically homogeneous crystals possess maximum resistance to degradation processes. In them,  the critical power of light destruction is determined by the self-focusing threshold of radiation in a material. Since the nonlinear addition to the refractive index Δn = n₂E² at the self-focusing threshold is determined by the change in the concentration of non-equilibrium carriers ΔN(E²), the value of the maximum fluctuation DΔN_max itself is proportional to the value of the non-equilibrium carrier concentration at the generation threshold ΔN_pores and the relative excess of the generation threshold J = (j – j_n)/j_n. Thus, a low threshold concentration of non-equilibrium carriers is one of the conditions for increasing material resistance to degradation processes. In doped crystals ΔN_pores is less than in  pure materials. This, perhaps, explains the rather higher value of P_critial  in the optimally doped homogeneous n-GaAs. Smaller values of P_critial in p-type samples doped with zinc can be associated not only with the inhomogeneity of these crystals, but also with large generation thresholds. In addition, the cross section for absorption of radiation by holes is about 3–4 times larger than by electrons, which can also reduce the self-destruction threshold of lasers. At Т = 300 K, the lasing thresholds are higher that naturally reduces the value of the self-focusing threshold.

It is a well-known fact, that corrosion of materials, as a phenomenon in the nature, is multifaceted, where its origin and development in many respects depend on environment micro-flora. In the modern world, corrosion is considered mainly as the spontaneous destruction of solids caused by chemical and electrochemical processes, developing on a body surface during its  interaction  with external environment.  The essence  of  corrosion  destruction   of objects  should be studied in aspect  of  the interrelated natural phenomena and processes that constantly occur  when an  object comes into contact with man-made environments and the environment containing many microorganisms of various genera and species. The accumulation and metabolism of microorganisms in surface defects of solids, when favorable physical, chemical and biological conditions are created in the contact zones, create areas of biocenosis in which metabolites, biogenic elements and chemically active radicals are formed, interacting with the contact surface of the body and the technogenic environment. Such interaction gives rise to the occurrence of both biochemical reactions in microbial cells and bioenergetic mechanisms of energy conversion on the contact surfaces, both in the microorganisms themselves and in the surrounding space. This initiator chemical, electrochemical and bio-corrosion processes of materials destruction. Consequently, the phenomenon of corrosion is presented as a system of interrelated microbiological and physicochemical processes of destruction of materials, arising from their interaction with the micro-flora of contact technogenic media and the environment. Based on the generalization and analysis of the results of the performed research work and taking into account the well known achievements and discoveries in the field of science and technology, the authors of the paper propose a new systematic approach and concept to the phenomenon of corrosive destruction of a solid with the account of the biological factor that initiates corrosion damage and destruction of materials.

The paper presents the technology of obtaining flat-conical lenses (axicons) by the method of free grinding a work-piece to a flat tool through a layer of abrasive suspension. For this, theoretical and experimental studies of the regularities of stock removal from the base of the cone and its lateral surface have been carried out. The processing modes have been identified that ensure both uniform operation of the flat surface of  the part and enhanced removal of  the allowance in the edge or central zone of this surface. During the study of the processing of the conical surface, the set-up parameters of the technological equipment have been established, at which there is a minimum deviation of the generatrix of the cone from straightness and maximum productivity of the process. The stages of processing conical lenses are proposed, which allow to assign the optimal sequence of operations in the manufacture of this type of parts from blanks of a cylindrical shape in cases where  the ratio of the height of the cone to the diameter of its base H/d £ 0.5. The main stages of processing include: grinding of the bases of cylindrical blanks with maintaining their mutual parallelism with a given accuracy; polishing one of the cylinder bases to achieve the required roughness and deviation from non-flatness; fastening a cylindrical blank to an auxiliary plane-parallel glass plate using molecular cohesion forces; mechanical fastening of a cylindrical work-piece with a collet adapter mandrel for a plane-parallel glass plate; applying the nearest sphere to the second base of the cylindrical blank; drawing a conical surface on the spherical part of a plano-convex lens; grinding and polishing the conical surface to achieve the required roughness  and straightness of the cone generatrix. The degree of efficiency of the setup parameters of the machine has been revealed depending on the technological heredity of the work-piece from the point of view of the distribution of the allowance to be removed over the machined surface.

 

A physical and chemical investigation of ceramic materials based on manganites of mixed rare earth elements  –  La0,8-хLnхCa0,2Mn0,94Cr0,04Ni0,02O3  –  for electrochemical and catalytic applications has been carried out, and   they were obtained from nitrate feedstock based on industrial-type polylanthanide concentrate, which corresponds to typical bastnaesite ore on the ratio of rare-earth elements in it. For polycrystalline samples of the obtained materials, the formation of single-phase structure or more often two-phase one has been identified after sintering in air at 1500 K, i. e., a the mixture of cubic perovskite phase based on low-cerium or A-site deficient manganite and a fluorite phase based on CeO2 with dioxide content of 54–98 %. A phase formation mechanism has been proposed, which is possible during the transition to compositions with rising cerium content at a constant sintering temperature of  manganite materials. The effect of the chemical composition and structure of the materials on their conductivity and density, reached by the sintering, has been established in the paper. Investigation of electrical conductivity has shown that in the manganites the semi-conductive behavior/ charge transfer mechanism (p-type) is realized at the temperature range of (300–1270) K. The maximum conductivity within the range of (290–1270) K is achieved in this low-cerium bastnaesite-type system for a two-phase material with the composition La0,8-хLnхCa0,2Mn0,94Cr0,04Ni0,02O3 at x= 0.6 and is 39 S/cm at a density level of 50 % of the theoretical one for a ceramic sample. Manganite materials with lanthanum substitution, such as investigated polylanthanide-based ones, can provide a lower cost for fabrication of electrochemical and other devices based on them, taking into account the complex prices dynamics on the markets of rare-earth raw materials during the last decade.

Тhematic Index

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