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This study investigates the effect of the mass ratio of aluminum to aluminum oxide on the structure and properties of Al–Al₂O₃ composite coatings deposited by cold spray deposition onto AISI 316L stainless steel substrates. Powder mixtures containing 70, 35, 30, and 20 wt.% Al₂O₃ were used to form the coatings, and the phase composition, microstructure, porosity, hardness, surface roughness, and tribological characteristics were studied using XRD, SEM/EDS, instrumental indentation, profilometry, and ball-on-disk testing. X-ray phase analysis confirmed the presence of metallic Al and α-Al₂O₃ without the formation of additional phases, while SEM analysis revealed continuous coatings with mean thicknesses ranging from 68.08 ± 1.16 to 103.39 ± 5.64 μm and an apparent porosity not exceeding 2%. The best structural and mechanical properties were observed for coating B3, prepared from a mixture of 30 wt.% Al₂O₃ and 70 wt.% Al: the porosity was 0.48%, the Martens hardness (HM) was 1757.6±155.8 N/mm², and the Vickers hardness was 211.8 ± 20.7 HV. Coating B3 was also characterized by a minimum surface roughness of Ra = 0.955 μm and a relatively stable coefficient of friction in the range of 0.55–0.60. The results obtained show that the composition of 30 wt.% Al₂O₃-70 wt.% Al provides the favorable combination of low apparent porosity, high mean hardness, and relatively stable friction behaviour among the specimens tested.

В работе исследовано влияние фракционного состава порошка Cr3C₂-NiCr и расстояния напыления на структуру, пористость и твердость покрытий, полученных методом высокоскоростного газопламенного напыления HVOF на подложке из стали 12Х1МФ. Для исследования были подготовлены пять образцов: B1 фракция порошка 0-20 мкм при расстоянии 300 мм, B2 – 20-30 мкм при 300 мм, B3 - 32-40 мкм при 300 мм, B4 - 32-40 мкм при 250 мм и B5 - 32-40 мкм при 200 мм. Микроструктуру покрытий изучали методом сканирующей электронной микроскопии, пористость определяли по SEM-изображениям с использованием программы ImageJ, элементное распределение оценивали методом EDS-картирования, а твердость измеряли с применением системы инструментального индентирования FISCHERSCOPE HM2000 в соответствии со стандартом DIN EN ISO 14577-1. Установлено, что увеличение фракции порошка при расстоянии 300 мм способствует росту толщины покрытия, однако может сопровождаться повышением пористости. Наибольшая толщина покрытия была получена для образца B5 и составила 253,14 ± 8,63 мкм, однако его пористость достигала 6,569 %. Минимальная пористость 2,909 % и наиболее высокая твердость были выявлены у образца B4: HM = 8063,2 ± 619,5 N/mm², HV = 1251,5 ± 107,1. Полученные результаты показывают, что оптимальным среди исследованных режимов является напыление порошка фракции 32-40 мкм при расстоянии 250 мм, обеспечивающее формирование более плотного и равномерного покрытия Cr3C2-NiCr. Ключевые слова: Cr3C2-NiCr; HVOF; фракция порошка; сталь 12Х1МФ; газотермическое напыление; SEM; пористость; твердость.

This study investigates the effect of high-temperature hydrogen exposure on the structure and properties of Cr₂O₃/Al₂O₃-based detonation coatings deposited on AISI 316L stainless steel. Bilayer and gradient coatings were exposed to hydrogen at 1000 °C for 3, 4, and 5 h and subsequently characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), surface profilometry, and thermal desorption spectroscopy (TDS). One independent specimen was examined for each combination of coating architecture and hydrogen exposure duration. Therefore, the present study was designed as an exploratory comparative investigation rather than a statistically powered study. The principal α-Al₂O₃ and Cr₂O₃ phases remained detectable after all exposure durations, indicating preservation of the main oxide phases. SEM/EDS analysis revealed microcracks, local defects, and heterogeneous surface regions, with more pronounced localized damage in the bilayer coatings. The Ra values of the bilayer coatings were 1.385, 0.833, and 1.207 μm after 3, 4, and 5 h, respectively, whereas the corresponding values for the gradient coatings were 1.049, 1.337, and 1.049 μm. The minimum Ra of 0.833 μm after 4 h in the bilayer coating coincided with SEM/EDS evidence suggesting local coating damage and possible thinning. TDS showed the most intense hydrogen desorption for the gradient coating after 3 h. Overall, the observed results suggest that coating architecture influences surface evolution and hydrogen-retention behavior under the investigated high-temperature hydrogen exposure conditions.

This study analyzes the effect of HVOF-sprayed Cr₃C₂-NiCr coatings on the thermophysical characteristics of superheater tubes of the BKZ-320-140 boiler unit. The influence of the protective coating on heat transfer processes, including convective and radiative heat exchange, as well as on the temperature state of the tube material under high-temperature flue gas conditions, is investigated. The temperature field was calculated using the finite element method in the ELCUT 6.6 software under transient heat transfer conditions. The model incorporates real operating parameters, including steam pressure and temperature, flow velocities, and thermophysical properties of materials. The results show that the presence of the coating leads to a slight increase in the total thermal resistance of the “tube wall–coating” system. However, its effect on the temperature regime and heat flux density is negligible. It is demonstrated that Cr₃C₂-NiCr coatings improve the corrosion and erosion resistance of heating surfaces without significantly reducing the thermal efficiency of the boiler unit under real operating conditions. The obtained results can be applied in design, modernization and optimization of power equipment in industrial energy systems of Kazakhstan.

В работе проведено комплексное исследование влияния технологических условий детонационного напыления на формирование морфологии, фазового состава и эксплуатационных свойств керамических покрытий на основе оксида хрома (Cr₂O₃). Покрытия формировались на подложках из нержавеющей стали AISI 316L с применением детонационного комплекса CCDS2000 при различных степенях заполнения ствола детонационной установки. С использованием методов рентгенофазового анализа, сканирующей электронной микроскопии, измерения микротвёрдости и шероховатости, а также трибологических и адгезионных испытаний исследовано влияние режимов напыления на структуру и свойства покрытий. Установлено, что во всех образцах доминирующей фазой является кристаллический α-Cr₂O₃. Показано, что изменение степени заполнения ствола существенно отражается на плотности, пористости и однородности микроструктуры покрытий. Оптимальные режимы детонационного напыления обеспечивают снижение пористости и шероховатости поверхности, повышение твёрдости, улучшение износостойкости и адгезионной прочности. Полученные результаты подтверждают возможность целенаправленного управления эксплуатационными характеристиками покрытий Cr₂O₃ путём оптимизации технологических параметров детонационного напыления. Это расширяет перспективы практического применения покрытий Cr₂O₃ в условиях повышенных механических и трибологических нагрузок в энергетике, машиностроении и других ответственных отраслях промышленности. Ключевые слова: детонационное напыление, покрытия Cr₂O₃, микроструктура, трибологические свойства, адгезионная прочность, морфология поверхности.

This study aims to compare the structural, mechanical, tribological, and corrosion properties of gradient and bilayer Al₂O₃/Cr₂O₃ coatings obtained by detonation spraying on 316L stainless steel. The coatings were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, instrumental indentation, scratch testing, ball-on-disk tribological testing, and potentiodynamic polarization in a 3.5% NaCl solution. The results showed that the gradient Al₂O₃/Cr₂O₃ coating had a denser and more homogeneous structure than the bilayer coating. Quantitative SEM image analysis showed that the apparent porosity decreased from 1.285% for the bilayer coating to 0.934% for the gradient coating. Instrumental indentation revealed an increase in hardness from approximately 401 HV to 462 HV and an increase in elastic modulus from about 173 GPa to 183 GPa. The gradient coating also demonstrated higher critical loads during scratch testing, indicating improved resistance to crack initiation and coating failure. Tribological tests showed a lower and more stable coefficient of friction for the gradient coating, decreasing from approximately 0.58–0.60 to 0.52–0.55. Potentiodynamic polarization measurements showed that the corrosion current density decreased from 0.50540 to 0.24155 µA/cm², while the corrosion rate decreased from 0.00894 to 0.00428 mm/year. These results demonstrate that the gradient coating architecture improves the performance of Al₂O₃/Cr₂O₃ coatings by reducing porosity, increasing structural integrity, and promoting an improved structural integrity and reduced defect-related stress concentration through the coating thickness. Therefore, gradient Al₂O₃/Cr₂O₃ coatings obtained by detonation spraying are promising for applications requiring enhanced wear and corrosion resistance.

In the present work, the influence of technological parameters of detonation sputtering, in particular the degree of barrel filling, on the properties of chromium oxide (Cr₂O₃) coatings was investigated. Coatings were obtained under different sputtering conditions and analyzed comprehensively using X-ray phase analysis, optical and electron microscopy, and measurements of microhardness, porosity, and tribological characteristics. The results showed that the degree of barrel filling significantly affects the microstructure, thickness, porosity, and mechanical properties of the coatings. The sample obtained at 58% barrel filling showed the lowest porosity (0.01%), uniform distribution of chromium oxide, and the best adhesion, which makes it possible to consider this mode as optimal for the formation of wear-resistant coatings by detonation spraying.