OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Ta b l e 2 Structural characteristics of the studied coatings Parameter NiCrBSi (PR-NKh17SR4) NiCrBSi (PR-NKh17SR4)+10 % B4C NiCr/WC (VSNGN-85) Average thickness, μm 410±15 390±40 430±30 Porosity, % 0.7±0.1 0.6±0.1 0.9±0.3 Hardness HV1 520±30 680±40 1,250±120 Fig. 4. EDS mapping of the cross-section of NiCrBSi (PR-NKh17SR4)+10 wt.% B4C The introduction of 10 % boron carbide resulted in a significant change in the microstructure (Fig. 3, b). While maintaining the average size of the structural elements and porosity at the same level (Table 2), a qualitative change in the boundaries between individual sprayed particles was observed. EDS analysis showed saturation of grain boundaries with boron and the total boron content close to the added one (see Fig. 4). At the same time, the content of boron carbide particles was significantly lower than in the initial mixture. This indirectly indicates partial decomposition of boron carbide and active interaction of boron with other components of the coating in the process. X-ray phase analysis also showed the presence of an amorphous peak and broadening of the base of the nickel peak, which confirms the formation of solid solutions in greater quantities compared to the NiCrBSi (PR-NKh17SR4) coating (see Fig. 5). For data processing and quantitative phase analysis, the Rietveld method implemented in the Match3 software was used, which allows for taking into account the overlap of peaks and the influence of microstructural factors. The NiCr/WC (VSNGN-85) coating has a characteristic “island” structure with clearly defined tungsten carbide particles in a nickel matrix (see Fig. 3, c). X-ray phase analysis also showed sharp peaks of tungsten carbide against the background of diffuse peaks corresponding to nickel-based solid solutions. The results of electrochemical studies showed a significant effect of the coating composition on their corrosion behavior in a 3.5 % NaCl solution. Potentiometric measurements revealed significant differences in the corrosion potential values (Fig. 7, a). The most noble potential (−250±30 mV) was recorded for the NiCrBSi (PRNKh17SR4)+10 % B4C coating, which indicates its increased thermodynamic stability. Analysis of the polarization curves (Fig. 6) revealed that the boron carbide-modified coating exhibited the lowest corrosion current density (0.8±0.02 μA/cm2), which was an order of magnitude lower than that of the base composition (6.5±0.2 μA/cm2). Electrochemical impedance spectroscopy confirmed the formation of a dense protective film on the modified coating surface, as evidenced by the high polarization resistance values (215±25 kOhm·cm² and low constant phase element parameters (45±5 µF·cm−2·s−1).
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