Influence of Gas Flow Rates in Kerosene-Fueled HVOF Spraying on the Microstructure, Phase Composition, and Corrosion Behavior of Cr3C2-NiCr Coatings

This study evaluates the relationship between combined HVOF operating conditions and the microstructure, phase composition, porosity, and electrochemical corrosion behavior of Cr3C2–NiCr (75/25 wt.%) coatings deposited on 12Kh1MF steel. Three kerosene-fueled HVOF regimes were compared by simultaneously varying oxygen flow (45, 54, and 63 scfh) and kerosene flow (25, 30, and 35 L/h), while maintaining a nominal fuel-to-oxygen flow ratio of 0.55, a spray distance of 300 mm, and a gun traverse speed of 8 mm/s. Coatings were characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, and quantitative image analysis of cross-sections. Electrochemical behavior was assessed by potentiodynamic polarization in 5 wt.% H2SO4 and 5 wt.% Na2SO4 at 25 °C. The coatings exhibited a dense lamellar structure, with mean two-dimensional areal porosities of 1.46 ± 0.067% (C1), 1.93 ± 0.106% (C2), and 1.15 ± 0.043% (C3). XRD identified Cr3C2, γ-(Ni,Cr), Cr3Ni2, and CrNi3 in all coatings; differences in peak intensities were interpreted qualitatively rather than as quantitative phase-fraction changes. In H2SO4, the measured corrosion current densities were 5.8222, 8.0681, and 5.4509 µA/cm2 for C1–C3, respectively; in Na2SO4, they were 3.5108, 3.1031, and 3.1528 µA/cm2. These results demonstrate that the measured electrochemical response depends on both the combined spraying regime and electrolyte composition, and that porosity alone does not explain the observed trends. The findings provide comparative process–structure–corrosion data to support further optimization of Cr3C2–NiCr coatings for steel components exposed to aggressive environments. Because the flow rates were varied simultaneously and the electrochemical results represent individual measurements, the findings do not establish independent effects of each flow parameter or statistical significance.