This study investigates the effect of low-temperature pulsed DC plasma nitriding on the surface properties of AISI 304 stainless steel for homogenizer valve-seat components. Plasma nitriding was performed in an ammonia atmosphere at 400, 440 and 480 °C for 8 h. The treatment led to the formation of expanded austenite at 400 °C, while higher temperatures promoted the formation of Fe-N and CrN-containing phases. The thickness of the modified layer increased from approximately 36 μm at 400 °C to 65 μm at 480 °C. Surface microhardness increased from 203 HV0.1 for the untreated steel to 652.6, 806.0 and 961.8 HV0.1 after nitriding at 400, 440 and 480 °C, respectively. The wear rate decreased markedly, reaching 1.92 × 10⁻⁵ mm³/(N·m) for DCPN480 compared with 30.65 × 10⁻⁵ mm³/(N·m) for the untreated sample. Among the nitrided samples, DCPN440 showed the most favorable corrosion behavior in 3.5 wt.% NaCl solution, indicating a balance between surface hardening and preservation of corrosion resistance. Numerical modeling confirmed that the strengthened surface layer can withstand equivalent homogenizer valve-seat loading without local plastic deformation. The results demonstrate that pulsed DC plasma nitriding can significantly improve the hardness and wear resistance of AISI 304 stainless steel while maintaining acceptable corrosion performance under optimized treatment conditions.

This work presents the development and experimental validation of a technology for producing WCCo metal-ceramic coatings by high-velocity oxygen-fuel (HVOF) spraying, intended for strengthening and restoring components of military equipment. The coatings were deposited on 12Kh18N10T stainless steel substrates at various spraying distances (300-400 mm). The microstructure, phase composition, surface roughness, microhardness, as well as the tribological and corrosion properties of the obtained coatings were investigated. It was established that the spraying distance has a decisive effect on the formation of the coating structure and its service properties. The optimal spraying regime ensures the formation of a dense lamellar structure with minimal porosity, preservation of the primary WC carbide phase, and limited decarburization to W₂C. It was shown that the microhardness of the coatings is 6-7 times higher than that of the base steel, while the friction coefficient and corrosion rate are significantly reduced compared to the substrate. The obtained results confirm the prospects of WC-Co HVOF coatings for improving the wear resistance, corrosion resistance, and operational reliability of military equipment components operating under high mechanical loads and aggressive environments.

This study investigates the effect of plasma spraying energy input on the microstructure and properties of APS-sprayed ZrO2-Y2 O3 (YSZ) coatings deposited on 12Cr18Ni10Ti stainless steel substrates. The coatings were produced under different spraying conditions by varying arc current, arc voltage, plasma gas flow, powder feed rate, and stand-off distance. A specific energy input to powder was used as a comparative parameter to characterize the thermal loading of particles during spraying. The microstructure of the coatings was examined by scanning electron microscopy, and porosity was evaluated from cross-sectional images using image analysis. Microhardness was measured under HV0.1 and HV0.3 loads, surface roughness was assessed using the Ra, Rz, and Rt parameters, and corrosion behavior was studied by potentiodynamic polarization in a 3.5 wt.% NaCl solution. The results show that spraying conditions significantly affect coating density, porosity, microhardness, roughness, and electrochemical response. The lowest porosity was obtained for the coating produced under intermediate spraying conditions and amounted to 3.2 ± 0.5 %, while coatings formed under lower and higher energy input exhibited porosity values of 4.5 ± 0.3 % and 6.7 ± 1.6 %, respectively. A decrease in microhardness with increasing porosity was observed, particularly at the HV0.3 load, due to the influence of interlamellar defects on the effective load-bearing area. The corrosion behavior of the coatings was found to depend not only on total porosity but also on defect morphology and pore connectivity. Overall, the results confirm that plasma spraying energy input strongly influences the structure and performance of APS-sprayed YSZ coatings and can be used to optimize spraying conditions. Keywords: atmospheric plasma spraying, YSZ coatings, energy input, microstructure, porosity, microhardness, roughness, corrosion behavior.

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.

In this study, an investigation was carried out to reduce the mass of a cantilever beam made of Al9 aluminum alloy using topology optimization (TO) based on the SIMP method. The optimization was performed with the APM FEM software package, which made it possible to implement numerical modeling at a modern level, taking into account the material features. The beam was subjected to a combined action of a concentrated vertical force of 4000 N and a longitudinal tensile force of 3000 N, which allowed simulating an actual operating load close to the working conditions of structures in mechanical engineering and construction. During the calculations, it was possible to reduce the mass of the structure by 52% while maintaining the main strength characteristics. At the same time, an increase in maximum stresses compared to the initial model was observed, which is associated with the redistribution of material and stress concentration in certain zones. However, the stress level remained within values close to those permissible for the chosen material considering the safety factor. Modal analysis confirmed sufficient separation of natural frequencies from critical values. The obtained results demonstrate the potential of applying TO for the design of lightweight, energyefficient, and technologically promising structures.

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: <20, 20–32, and 32–40 μm. Individual spray parameters were selected for each material to ensure high-quality deposition (standoff distance 350 mm, one pass for WC–12Co; 250 mm, two passes for Cr₃C₂–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 <20 μm fraction); for Cr₃C₂–NiCr, oxidation and carbide dissociation prevail (in the <20 μm fraction—13.7% Cr₂O₃ 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.