The Influence of Powder Composition and Hydrogen Consumption on the Structural, Corrosion and Tribological Characteristics of Fe-Cr-Al Coatings Obtained by Air Plasma Spraying

Fe-Cr-Al coatings were obtained by air plasma spraying (APS) from 85Fe-12Cr-3Al and 68Fe-26Cr-6Al powders at two hydrogen flow rates (8 and 13 L/min), which resulted in four deposition regimes (A1, A2, B1, B2). Stainless steel 20Kh13 (equivalent to AISI 420) was used as the substrate material. The microstructure of the coatings has a typical lamellar layering with molten and semi-molten particles. When the hydrogen flow rate is increased to 13 L/min, a denser and more homogeneous structure with reduced porosity is observed. X-ray phase analysis revealed the presence of metal and oxide phases (Fe,Cr), Fe₃O₄, FeO, Fe²⁺Cr₂O₄, which indicates partial oxidation of particles during the spraying process and stabilization of the structure. Electrochemical tests in 3.5% NaCl solution showed that the 85Fe-12Cr-3Al coatings are characterized by a corrosion potential of E_o ≈ -0.60…-0.67 V, a corrosion current density of i_o = (2.6-4.7) × 10^-5 A/cm², and a corrosion rate of 0.30-0.55 mm/year, whereas the 68Fe-26Cr-6Al coatings exhibit lower values of i_o = (1.4-2.9) × 10^-5 A/cm² and a corrosion rate of 0.17-0.34 mm/year, indicating the formation of a denser protective oxide film (Cr₂O₃ + Al₂O₃) and enhanced surface passivation. Tribological tests showed that 85Fe-12Cr-3Al coatings demonstrate more stable friction compared to 68Fe-26Cr-6Al, while for regime B2, after 180 m, an increase in the friction coefficient is observed, caused by brittleness and the local destruction of the oxide film. A comprehensive analysis of the results showed that increasing the hydrogen consumption to 13 L/min improves the density and corrosion-tribological characteristics of the coatings.