Zh. Bakyt

HVOF coatings based on tungsten and chromium carbides are widely used in aerospace, energy, and oil and gas industries. However, the selection between the wear resistance of WC–Co and the corrosion resistance of Cr₃C₂–NiCr is often hindered by a lack of systematic data on the effect of powder particle size. In this study, WC–12Co and Cr₃C₂–NiCr coatings were deposited onto 12Kh18N10T stainless steel substrates by HVOF spraying using three particle size fractions: 3C₂–NiCr). The influence of powder particle size distribution on coating properties was investigated using a comprehensive set of methods, including scanning electron microscopy, X-ray diffraction with Rietveld quantitative phase analysis, microhardness testing, tribological testing, electrochemical measurements, and numerical modeling of particle in-flight motion. It was found that the 20–32 μm fraction is optimal for both materials. Different degradation mechanisms were identified: for WC–Co, decarburization of WC with the formation of W₂C and η-phases dominates (maximum for the 3C₂–NiCr, oxidation and carbide dissociation prevail (in the 2O₃ and 38.6% Cr₇C₃), leading to low coating thickness (~16 μm) due to loss of ductility and wettability. Numerical modeling confirmed that the high velocity of fine Cr₃C₂–NiCr particles (~680–720 m/s) does not compensate for their overheating, whereas for WC–12Co all fractions have velocities above the critical threshold, but coarse particles (32–40 μm) give porosity up to 3.15% due to insufficient deformation. Corrosion tests showed that under spraying conditions optimized for each material, the Cr₃C₂–NiCr coatings (corrosion rate 0.066–0.102 mm/year) are an order of magnitude superior in corrosion resistance to WC–12Co coatings (corrosion rate 0.353–0.651 mm/year), owing to the passivation of the γ-Ni(Cr) matrix; for WC–Co, the main protective barrier is provided by the structural density.

Electrolytic-plasma hardening of steel components requires reliable non-contact temperature monitoring, but traditional pyrometry is complicated by the variable emissivity of steel and the intense radiation of the plasma envelope. This work presents an approach that repurposes a compact multispectral AS7341 sensor into a virtual temperature sensor based on physically grounded spectral feature engineering and regularized machine learning. The use of logarithmic ratios of the near-infrared channel (940 nm) to the visible channels suppresses the plasma contribution and linearizes Wien’s radiation law. On a controlled dataset of 20 cycles, this increases the Pearson correlation with the peak temperature from r = 0.498 (raw NIR channel) to r = 0.781 for the log(NIR/Clear) feature. Current is identified as a confounding variable; normalizing the NIR/Clear ratio by the cycle-averaged current (r = 0.761) ensures correct signal interpretation under varying process conditions. Two narrow channels–NIR (940 nm) and F8 (680 nm)–provide accuracy equivalent to the broadband Clear channel (r = 0.778 vs. 0.781), thus simplifying hardware implementation. Ridge regression using three weakly correlated features (log(NIR/Clear), cycle duration, and initial temperature) achieves a mean absolute error of 91.4 °C under leave-one-out cross-validation (LOOCV) and 85.5 °C on an independent current-group test (R² = 0.536). Independent verification by scanning electron microscopy and Vickers microhardness on 30KhGSA steel confirms reliable separation of the three thermal regimes: underheating (900 °C, 540–590 HV). The proposed set of spectral features provides a physically justified basis for a low-cost industrial temperature sensor for electrolytic-plasma processing.

This article presents a comprehensive examination of the electrolytic-plasma hardening (EPH) process applied to 20GL structural steel, a material frequently used in the automotive, transport, and various other industries. The relevance behind this research lies in the necessity to enhance the performance of steels that face high mechanical loads, elevated temperatures, and corrosive environments. Experimental findings reveal that electrolytic-plasma treatment substantially increases the hardness of 20GL steel to approximately 600 HV on average. Additionally, prolonging the heating duration contributes significantly to greater hardness, playing a decisive role in bolstering wear resistance under load. Microstructural analysis confirms the formation of a fine-grained martensitic phase, highlighting the steel’s transformation and strengthening. Furthermore, the study emphasizes that the chemical composition of 20GL steel influences the hardness gradient from the surface inward and leads to the development of finer-grained features in the steel’s microstructure. Overall, the electrolytic-plasma process proves beneficial not only for improving mechanical attributes but also for enhancing reliability and service life of critical components. From an industrial standpoint, this technology is notable for its adaptability and cost-effectiveness, making it an attractive solution for sectors such as automotive manufacturing, construction, and the energy industry. Thus, electrolytic-plasma hardening emerges as a forward-looking method aligned with modern engineering demands, offering a promising avenue for advanced material optimization.

The study is devoted to a detailed analysis of the effect of the voltage level used in the microarc oxidation process on the tribocorrosive properties of calcium phosphate coatings formed on titanium substrates. The paper considers various voltage values (100 V, 200 V, 300 V), which were used to create coatings with unique morphological, structural and physicochemical characteristics. These features, in turn, have a significant impact on the mechanical properties of the coatings, their wear resistance and corrosion resistance. The research methodology includes profilometry for detailed analysis of surface texture, microhardness measurement for evaluation of mechanical properties, tribological tests for wear resistance, and potentiodynamic studies in saline solution to evaluate the level of corrosion resistance of coatings. The obtained results will provide an opportunity to better understand the mechanisms of influence of microarc oxidation parameters on the formation of calcium phosphate coatings and their performance characteristics. This, in turn, will be useful for the development of new materials with improved functional properties that can find wide application in the biomedical field, including the production of implants, as well as in industry where high corrosion resistance of coatings is required.

This article evaluates the electrolyte-plasma hardening (EPH) of steel 45 using an electrolyte based on sodium carbonate (Na₂CO₃). Theoretical foundations of the electrolysis process of a sodium carbonate aqueous solution were studied during the course of the work. The mechanical and tribological properties of 45 steel samples after EPH were studied. It was found that with an electrolyte composition of 20% Na₂CO₃ and 80% distilled water, a hardened zone with a thickness of up to 5 mm is formed after EPH. The increase in microhardness reached up to 690 HV, which corresponds to a 3–3.5 times increase compared to the initial state. The results of tribological tests showed that the friction coefficient of steel 45 decreased after EPH, indicating a significant improvement in tribological characteristics compared to the initial value before hardening. Electrochemical tests on the corrosion resistance of steel 45 were also carried out. After EPH, the corrosion rate significantly decreased for steel 45 samples, indicating its highest corrosion resistance.

The article examines the effect of electrolytic plasma hardening on the wear resistance and corrosion resistance of steels 45 and 65G, which are used in the production of agricultural machinery components. The presented results demonstrate the improvement of the surface properties of steel through the application of electrolytic plasma hardening. This technology provides rapid heating and cooling, which contributes to the formation of a fine-grained and hardened surface layer, as evidenced by microstructural studies conducted using an optical metallographic microscope. Tribological tests showed an improvement in wear resistance after electrolytic plasma hardening: the wear volume for steel 45 was 3,03×10^-4 mm³, and for steel 65G it was 6,17×10^-5 mm³, which is 7 and 4,5 times less than the wear volume for the initial samples, respectively. The analysis of polarization curves showed that the corrosion current density decreased compared to the initial sample. For steel samples 45 and 65G after three cycles of electrolytic plasma hardening, the corrosion current densities were 6,87×10^-6 A/cm² and 1,61×10^-7 A/cm², respectively. Additionally, a shift in the corrosion potential towards more positive values was noted, indicating an increase in corrosion resistance. The results of the study demonstrate significant improvements in the tribological and corrosion properties of steels 45 and 65G after electrolytic plasma hardening, providing valuable data for industrial applications.

The effect of protective coating applied to steel 45 made of 30HGSA wire by electric arc metallization on corrosion resistance compared to untreated steel 45 was investigated. The test methodology included electrochemical analyses such as polarization curves. The results showed that steel 45 coated with 30HGSA wire shows significantly higher corrosion resistance compared to standard steel 45.The result of this study confirms the significance of electric arc metallization technology as an effective way to improve the corrosion resistance of steels. The application of protective coating of 30HGSA wire on steel 45 not only improves its characteristics, but also provides opportunities for more durable use in aggressive environments. Also, these methods can be adapted for other types of materials, which opens new perspectives in the field of steel structures protection. This research can serve as a basis for the development of new norms and standards in metal fabrication and processing. These results provide valuable scientific data that can contribute to the development of improved corrosion resistant materials for applications in critical industries such as oil and gas, marine and construction projects, and mechanical engineering, where material reliability is a key factor.

The article considered the application of the organic Rankine cycle, in particular attention was paid to the correct choice of the working fluid in installations that implement such a cycle.The choice of a working medium for solving generalized tasks is the determining basic condition for the effectiveness of the implementation of the organic Rankine cycle. In addition, the article formulates the working bodies used in the cycle and the requirements for working bodies. The properties of the working bodies used in the organic Rankine cycle were studied and the main factors affecting the effective functioning of the cycle were noted. The main properties of working fluids and their comparison with water are given. The effectiveness of the organic Rankine cycle and its features were also studied with the optimal choice of the working fluid, a SWOT analysis of the overall cycle was carried out.The article presents the results of the study and recommendations on the choice of a working fluid for the organic Rankine cycle in thermal power engineering. Research shows that the choice of working fluid depends on a number of factors, such as temperature conditions, desired level of efficiency, environmental impact, availability, safety, etc. Considered data can be useful to specialists in the field of thermal power engineering when choosing the optimal solution for a specific installation.