International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

This work presents a brief overview of the essence, principles and technological features of reactive electrospark processing (RESP), based on a simple, economical and ecological method – electrospark deposition (ESD), which avoids many of the disadvantages inherent in other existing methods. This treatment can optimize the physicochemical properties of the substrate surface and improve the structure, hardness and wear resistance. The application of RESP technology in surface modification of titanium alloys is considered. Research results, including those of the authors of this work, are presented, which demonstrate the possibilities of RESP for reducing
roughness and surface defects and for the synthesis of new phases and ultrafine structures that are not present in the electrode and substrate. The effect of RESP technology on the wear resistance of titanium and titanium alloys is shown. The main dependences of the quality and properties of the treated surfaces on the process parameters are identified, and ways to form reaction phases, to avoid and remove surface defects and to obtain “in-situ” new intermetallic and wear-resistant compounds are presented. The possibilities and prospects for the use of RESP to improve the surface characteristics and properties of titanium and its alloys are indicated.

The physic-technological basis for fabrication of bulk rods and plates of amorphous, amorphous-nanocrystalline and 100% nanocrystalline alloys at melt cooling rates from 80 to 3200 K/s with crystal sizes from 10 to 50 nm has been developed. The multiphase structure formed in the initial bulk samples, as well as in the process of nanocrystallization of amorphous ribbons, is characterized by record microhardness values of 17-22 GPa. Amorphous powders (20-100 μm) of Fe55Ni8Co6Mo4Cr2V1Al2P9C6B5Si2 and Fe61.37Co6.84Cr3.78V0.85W0.82Mo1.06Nb0.85B19.87C1.99Si2.57 alloys are used to create a wear-resistant coating on structural stainless steels and low-carbon St3 by the gas-thermal “cold” method » sputtering and subsequent melting of the applied layer.The values of microhardness (Hμ) of nano-coatings significantly exceed the microhardness of all known tool steels. Examples of technology transfer and practical using of developed amorphous and nanocrystalline alloys are presented.

Commonly used metallic biomaterials are titanium and its alloys, cobalt-based alloys and 316L stainless steel. Titanium alloys are reference materials in biomedical applications due to their desirable properties such as excellent mechanical properties and good biocompatibility. Since presence of different metals can significantly alter the properties of titanium it is usually alloyed with other metals, including the zirconium. In this work Ti-20Zr was prepared by powder metallurgy by mixing the powders in a ball mill and sintering in a tube furnace under argon atmosphere. Microscopic analysis with the light microscope showed that the porosity decreased with increasing temperature and sintering time. Scanning electron microanalysis with energy-dispersive spectrometry showed the two-phase microstructure of the sintered alloy. Microhardness was determined by Vickers method. A longer sintering time and a higher sintering temperature resulted in higher microhardness values.

This work discusses the properties of 3D titanium alloys with wear-resistant coatings of hard alloy electrodes based on WC-TiB2-B4C and solder mass of Co-Ni-Cr-B-Fe-Si-C, produced by reaction electrospark processing (RESP) at positive and negative polarity. Through profilometric, metallographic, XRD, SEM, EDS and tribological methods, the complex influence of polarity and pulse energy on the topography, composition, properties, and wear characteristics of the coated surfaces was investigated. The differences in the coatings obtained with the two polarities were identified. Coatings with similar roughness and thickness were obtained, which can be changed by changing the modes for RESP within the limits Ra =2.5÷5μm, δ= 8÷40μm, with microhardness 8 to 14 GPa and 2-4 times higher wear resistance than that of the substrate. At RESP with negative polarity and pulse energy up to 0.04 J, the coatings have comparable characteristics and properties to those at positive polarity, but lower roughness, finer structure and lower coefficient of friction. These coatings can be successfully used to reduce roughness and surface defects and improve the wear resistance of 3D titanium alloys. The pulse energy and polarity of RESР, producing coatings with minimum roughness and maximum wear resistance, have been determined.

Titanium as a raw material for production is very expensive due to its high price and the complex production process. One of the successful alternatives for the production of titanium alloys and final products is powder metallurgy technology. In this work, a Ti-20Zr alloy for biomedical applications was produced using the powder metallurgy process. The density values determined for the compacts depend on the compression pressure. Namely, the compressibility of the powder mixture increases with increasing compaction pressure. A higher sintering temperature as well as a longer sintering time are more favourable to obtain higher values for the sintered density. Similarly, the compression coefficient is lower for samples compacted at higher pressure, while its value increases with increasing sintering temperature. The volume change in the volume of the sample is more pronounced after sintering at higher temperature and shorter time.

Comparative experimental studies of the mechanical characteristics of polycrystalline aluminum alloy AMg6 and nanocomposite  based on it n-AMg6/C60 during tension tests, as well as the effect of strain hardening on these characteristics during multi—cycle loadingunloading processes up to the destruction of the sample, are presented. The limits of strength and ductility, as well as the hardness and, by ultrasonic method, all independent second order elastic coefficients were measured.

The influence of high-carbon ferrochrome on the features of structure formation and properties of chromium carbide steels based on the Fe-FKh800 system was investigated. It was shown that the optimal combination of hardness and tensile strength with sufficient crack resistance has a carbide base of 65% Fe – 35% (wt.) FKh800. A typical microstructure of sintered carbide is a metal matrix composite consisting of chromium steel of composition close to Kh17 and double carbide (Cr0.799Fe0,201) 7C3. The effect of TiB2 additive on the structure, phase composition, mechanical and tribotechnical properties of materials based on the Fe- 35 (%,wt.) FKh800 system was also investigated. Additions of titanium borides in the amount of 0.38-1.48 (% wt.) leads to some increase in hardness, noticeable increase in the flexural strength and leads to increase wear resistance of carbidosteels.

To create a high-hardness and wear-resistant coating on the heat-resistant aluminum AK4 alloy, the technology of microarc oxidation is used. The possibility of forming an oxide layer on the surface (mainly of α−Al2O3 and γ−Al2O3 phases) with a thickness of about 150 μm and a hardness of 17000 – 18000 MPa is shown. For this, the process of microarc oxidation was carried out at a current density of 20 A/dm2 in an electrolyte of the composition KOH (1-2 g/L) and Na2SiO3 (6-12 g/L). The obtained properties of MAO coatings on the AK4 alloy make it possible to effectively use such materials for engine elements.

The effect of TiB2 additives on the sintering temperature, structure, and mechanical properties of materials based on the Fe-FeCr800 system is investigated. It was shown that the introduction of titanium diboride additives leads to the activation of compaction and to a 50–70ºС decrease in the sintering temperature of the pressed composites based on iron. It has been studied that the addition of titanium diboride in the range of 0.38-0.74 (% wt.) provides, with a slight increase in hardness, an increase of 20-25% of the flexural strength of the composite 65Fe-35 FeCr800800 (% wt.), and also provides the formation of a multiphase, microheterogeneous structure of the matrix-filled composite type, which consists of chromium steel of the X6Cr17 type, double iron-chromium carbides M7C3, M3C and complex carboborides of the Me3(CB) type.

Physicomechanical and adhesion characteristics, specific surface energy of vacuum coatings formed on high-speed steels of the P6M5 type subjected to processing at cryogenic temperatures are investigated. The structural transformations occurring in vacuum coatings formed on steel substrates with subsequent processing at low temperatures were studied. A change in the tribological characteristics of titanium nitride coatings during subsequent processing in a cryogenic liquid is shown.

The influence of temperature of sintering on structure formation, phase composition, microhardness of components of powder composite 65 % wt. Fe – 35 % wt. FH800 were investigated. It has been established that the increase in the temperature of sintering from 1050 ºС to 1250 ºС leads to some increase in volumetric shrinkage, density and decrease in porosity of samples of material which was made from coarse-grained source powders of industrial production components. It was found that the sintering of green compacts in the range of 1000-1300 ºС causes significant changes in the chemical and phase composition of the carbide component of the composite, which are described by a series of phase transformations: M7C3 → M3C (1000-1150 ºС) → M7C3 (1200 ºС) → M3C (1250-1300 ºС)

Surface saturation with boron of Fe-C-Cu construction powder materials aims to improve the surface hardness of the articles and hence improve wear, contact strength and other mechanical properties. This study investigates the influence of single-component diffusion enrichment modes with boron of semi-permeable powder metallurgical samples from the Fe-C-Cu system. The powder samples on the basis of iron powders NC 100.24 to which 0,3 ÷ 2,5% Cu and 0,4% carbon were added were subjected to the study. Diffusion saturation with boron was carried out in semi-permeable saturation media with a composition of 84% Na2B4O7 + 12% SiC + 4% K2Cr2O7 at temperatures 850 ÷ 950 ° C for 2 ÷ 4 hours. Graphical dependencies are presented for the variation of the diffusion slit thickness in the longitudinal section of the test samples depending on their density, duration and saturation temperature. The experimental results obtained are compared with those obtained by combining pure iron samples with the same technological parameters.