Bulletin PNRPU. Mechanical engineering, materials science

An overview of methods for producing ceramic-metal composites (cermets), based on titanium carbide and iron, which are also called carbide-steels and ferrotics. It is shown that the traditional methods of powder metallurgy and foundry technology are long-term and energy-intensive. The results obtained earlier are presented to use the process of self-propagating high-temperature synthesis (SHS) for obtaining TiC-Fe and Al2O3-TiC-Fe cermets both from elemental powders and from oxides by aluminothermic reduction. Own results on coupling of reactions of SHS of titanium carbide and reduction of iron from oxide by aluminum (aluminothermic reduction) and carbon (carbothermic reduction) are described in more detail. It is shown that in the case of aluminothermic reduction, it is advisable to use as a charge (Ti+C)+x(Fe2O3+2Al) a mixture of thermite (Fe2O3+2Al) and carbide (Ti+C) granules, separately prepared from the original powders. In the case of carbothermic reduction, there is no need to granulate the charge from a total mixture of powders (Ti+C)+x(Fe2O3+3C). The combustion of these SHS charges proceeds quietly in a simple open-type reactor in an air atmosphere, without ejections of the initial reactants and products of SHS. Combustion products are highly porous, easy-to-grind cakes of Fe(Al)-Fe3Al-Al2O3-TiC or Fe-TiC cermet powders. Presented applications of the coupled combustion process are distinguished by energy saving, simple technology and equipment, cheap source components, good properties of the synthesized cermet powders, that determines the prospects of the organization of their competitive industrial production for use as abrasive materials, wear-resistant coatings, the initial powders for fabrication of compacted wear-resistant components and billets by powder metallurgy.

The possibility of using selective laser sintering (SLS) to obtain gradient porous and compact porous powder structures by surface melting of powder particles while maintaining a solid core is shown. In order to study the kinetics of contact formation, it was proposed to assume the minimum energy value of a single laser pulse as the value at which a certain structural element having a diameter equal to the diameter of the laser beam focal spot and the thickness equal to the powder particle average diameter, is obtained. The temperature distribution on the surface of the VT1-0 titanium powder structural element of the fractional composition (-0.315+0.2) mm and (-0.4+0.315) mm was investigated when exposed to a single laser pulse of various power and duration. It is shown that the powder particles in the central zone of the focal spot are heated to temperatures of 1900-2000 K, while particles outside this zone are heated to temperatures of only 900-1000 K and do not participate in the process of contact formation. Established the ranges of SLS technological modes, under which stable contact formation of titanium powder particles of the studied fractional compositions takes place. The possibility of forming gradient porous and compact porous powder structures by controlling the parameters of pulsed laser exposure was experimentally shown. It has been found that accurate dosing of energy and the number of pulses of laser radiation results in minimal shrinkage of powder layers within the absence of particle conglomeration, control the structural characteristics and properties of products, microstructure and phase composition preservation of the original materials. The technology allows providing intralayer and interlayer powder sintering of different fractional compositions with a given structure gradient with minimal disruption of the initial geometry of the particles.

The work is devoted to the study of the mechanism of shock-abrasive wear (AIM) as one of the poorly studied types of mechanical wear. Machines and mechanisms of the oil, mining, construction and road sectors are more susceptible to abrasive wear. One of the ways to improve the wear resistance of materials subjected to AIM is the introduction of alloying elements into their composition. The influence of the chemical composition of the powder material on impact-abrasive wear resistance was determined and the effectiveness of the introduction of carbon, nickel and chromium into the powder materials was substantiated. The analysis of existing works and conducted studies have shown that increasing the wear resistance of compact and powder steels by known methods does not provide them with the necessary combination of properties. The paper shows the possibility of increasing the shock-abrasive wear resistance of compact and powder materials due to the damping of impact energy in composite samples consisting of layers of wear-resistant steel and an elastic-dissipative substrate. It has been established that the use of elastic substrates reduces the wear of a composite material due to the absorption and dissipation of the impact energy. A feature of the AIM mechanism of a composite material with the use of an elastic-dissipative substrate and the influence of its properties on the wear rate are disclosed. To study the impact-abrasive wear resistance of a composite material, samples were made consisting of a layer of wear-resistant steel and an elastic damping layer. The elastic damping layer was attached to the wear-resistant layer using hot and cold vulcanization technology. Testing of composite samples on AIM was carried out on a special installation. Further research directions are identified.

In this work the structure, elemental and phase composition of the diamond-matrix transition zone of a diamond tool for dressing abrasive wheels, fabricated using a new hybrid technology were studied. The hybrid technology consists in combining processes of diamond thermal diffusion metallization with carbide-forming metals and sintering of diamond containing matrix based on carbide powder mixture with copper impregnation in one operation cycle (heating and cooling) of a vacuum furnace. In the hybrid technology, each diamond grain is tightly wrapped in a thin copper foil with carbide-forming metal powder distributed around diamond grains. Due to compact arrangement of carbide-forming metal powder particles around the diamond grains and the shielding effect of copper foil favorable conditions are created that ensure the effective thermal diffusion metallization of the diamond during the sintering of the matrix. It was established by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy, that a metallized coating chemically bonded to diamond is formed on the diamond surface, which provides durable diamond retention in copper-impregnated carbide matrix at given temperature-time regimes and the sintering conditions specified in the experiment. In this case, the structure and microhardness of the matrix, with the exception of the areas immedi- ately adjacent to the diamond-matrix transition zone, remain the same as the matrix of the carbide powder mixture sintered in the absence of chromium. Comparative tests of the same type of ruling pencils were carried out, which showed the high efficiency of the hybrid technology for obtaining diamond-containing composites for instrumental purposes. An increase in the value of the specific productivity of the diamond pencil produced by the hybrid technology was achieved by 44.66 % compared to the same indicator of the same type diamond pencil obtained according to the traditional sintering scheme without the metallization of diamond grains.

The purpose of the study is to improve the performance characteristics of powder pseudo-alloy materials using surface heat treatment. Such materials have unique properties, for example, self-lubrication under dry friction conditions, high thermal conductivity coefficient, and high electro-erosion resistance. The disadvantage of powder pseudo-alloys is their relatively low strength. The paper considers the method of surface hardening by high-energy treatment - laser radiation. The paper describes the method of experimental research, describes the method of obtaining powder material, its chemical composition, shows the equipment used. The results of studies of the microstructure and microhardness of the surface layer of steel-copper powder pseudo-alloy after laser heat treatment (LHT) of a continuous-wave fiber laser with a maximum power of 1 kW are given, LHT modes are indicated, the influence of LHT parameters on the characteristics of the hardened layer is evaluated, a nomogram is given for selection technological regimes of LHT (laser radiation power, beam diameter and speed of movement), allowing to obtain the required microhardness and depth of the hardened layer by specifying a certain power density value. The correctness of the appointment of technological regimes using nomograms verified by experimental studies. The distribution of microhardness over the depth of the hardened layer, as well as the dependence of the microhardness on the depth of the hardened zone in various LHT modes, is shown. It has been established that the microhardness of the surface layer after LHT reaches 900-1000 HV (67-69 HRC), which significantly exceeds the hardness values obtained by classical volumetric heat treatment (43-45 HRC), which is associated with higher heating and cooling rates when using laser radiation as a heat source.

This paper presents the experience of developing the production technology of copper-chromium composite material, which is used for the manufacture of electrodes of high-voltage vacuum switching devices. The difficulties in creating such composites are related to the need to meet various and often mutually contradictory requirements for materials of contacts for switching current in vacuum. These materials must have high electrical conductivity and thermal conductivity; have high mechanical strength and hardness, both at room temperature and at elevated temperatures; to have a minimum tendency to welding and sticking in contact during the passage of a strong electric current; to contribute to the rapid recovery of the electrical strength of the vacuum gap after breaking the contact and quenching the vacuum arc. A comparison of the materials obtained by different technologies, in particular those obtained by sintering in a vacuum, in a reducing atmosphere and by electric arc melting, is presented. The specific resistance of composites was evaluated using a model of a two-component mixture of randomly distributed grains of components. Methods of powder metallurgy allow to obtain composite materials from such non-forming alloys of metals as copper and chromium, which best meet the requirements for electrical contacts of high-current vacuum equipment. Composites are produced by cold pressing of powder mixtures of electrolytic copper and aluminothermic chromium followed by sintering in vacuum. It have better electrical conductivity compared to the materials produced by electric arc melting. Developed in the Centre of Powder Material Science (Perm National Research Polytechnic University) copper-chromium composite Cu65Cr35 is used as billets for the contacts arc chambers series KDVK, KDVN etc.

The distinctive ability of ultra-high-temperature ceramics (UVTK) is its ability to be exposed to prolonged exposure to oxidizing environments at temperatures up to 2000 °C, without losing its strength characteristics. It is this property that makes this type of material promising for use in the aerospace and energy industries. One of the most well-known ultra-high-temperature materials are borides based on zirconium and hafnium, dispersion strengthened by particles of silicon carbide and refractory compounds (silicides, carbides, nitrides). At the moment, zirconium diboride is one of the most well-known materials among ultrahigh-temperature ceramics due to its high melting point (3245 °C), high thermal conductivity, good heat resistance, low thermal expansion coefficient, retention of strength at elevated temperatures and stability in extreme environments. In this work, the effect of rare-earth elements on the sintering processes of materials based on ZrB2 - SiC (20 vol.%) Obtained by the method of plasma spark sintering is investigated. Composite ceramic materials based on ZrB2 - 20 vol.% Were obtained at the plasma spark sintering unit at a temperature of 1700 °C. % SiC with the addition of oxides of rare earth elements, the content of which ranged from 0 to 5 vol. %. The isothermal holding time was 3-5 min, the pressing pressure was 30 MPa. It is established that an increase in the time of isothermal exposure leads to a decrease in porosity. The influence of the content of oxides of rare-earth elements on the compaction processes during sintering of ultra-high-temperature ZrB2-SiC-based ceramics, the microstructure and the phase composition is investigated.