OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Fig. 2. Particle size distribution of the initial powders and mixture gauge 45MG (Olympus, Japan). The particle size distribution of the initial powders and mixture was determined using an Analysette 22 NanoTec Plus powder granulometry analyzer (Fritsch, Germany), as shown in Fig. 2. The investigation of the obtained coatings was performed using a comprehensive set of modern analytical methods to thoroughly evaluate their structural and functional properties. Microstructural studies were conducted using a Mira 3 scanning electron microscope (Tescan, Czech Republic) equipped with an X-Max 50 energy-dispersive spectroscopy system and AZtec software (Oxford Instruments, UK). Secondary electron (SE) and backscattered electron (BSE) imaging, along with elemental composition analysis, were performed at an accelerating voltage of 15 kV and a working distance of 15 mm. The EDS data were processed using specialized AZtec software. Porosity evaluation was carried out by analyzing SEM images of coating cross-sections with a 1,000 μm field of view using ImageJ software. The phase composition of the coatings was examined by X-ray diffraction analysis using an ARL X’TRA diffractometer with Cu-Kα radiation (λ = 1.5418 Å). Measurements were performed in θ-2θ scanning mode within the angular range of 10–90° with a step size of 0.02° and an exposure time of 1 s per point. Phase identification was conducted using the PDF-2 database from the International Centre for Diffraction Data (ICDD). Corrosion testing was performed using a three-electrode electrochemical cell with a SmartStat PS-10-4 potentiostat-galvanostat. A 3.5 % sodium chloride solution (pH = 6.8±0.2), prepared from analytically pure (“chemically pure”) grade reagent and distilled water, served as the working electrolyte. The reference electrode was a silver/silver chloride (Ag/AgCl) electrode, and the counter electrode was made of graphite. The electrochemical testing protocol consisted of several sequential stages. Initially, the open circuit potential (OCP) was monitored for 60 minutes until it reached a steady-state condition (±10 mV/10 min). This was followed by electrochemical impedance spectroscopy (EIS) measurements across a frequency range of 50 kHz to 10 mHz with an AC signal amplitude of 10 mV. The obtained Nyquist spectra were fitted using equivalent electrical circuits with the “impedance.py” script [21]. Subsequently, potentiodynamic polarization curves were recorded at a scan rate of 1 mV/s, covering a potential range from −300 mV versus OCP to +1.2 V versus Ag/AgCl, or until reaching a current density of 10 mA/cm2. Special attention was paid to analyzing the Tafel regions of both anodic and cathodic branches to determine kinetic parameters of the corrosion process. For each sample, a minimum of three replicate tests were conducted, followed by statistical analysis of the results. Post-corrosion characterization included surface examination using scanning electron microscopy. The depth of corrosion penetration was evaluated using a confocal laser microscope with a vertical resolution of 10 nm. Mechanical tests involved Vickers microhardness measurement criteria on a NEXUS 4504-IMP hardness tester (INNOVATEST, Netherlands) at 1 kg and a holding time of 15 s. For each sample, at least 10 measurements were made with subsequent exclusion of gross errors using the Student criterion. Results and Discussion A comprehensive study of the coating microstructure revealed significant differences between the studied compositions. The coating based on the self-fluxing powder NiCrBSi (PR-NKh17SR4) demonstrated
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