Corrosion Resistance of VC–FeCr and VC–FeCrСо Coatings Obtained by Supersonic Gas-Flame Spraying

Abstract

We study coatings of the VC–FeCr system with a thickness of 100 μm on a substrate of D16 aluminum alloy deposited by the method of supersonic gas-flame spraying (High Velocity Oxygen Fuel Flame Spraying Process; propane–oxygen fuel). For comparison, we apply the method of plasma spraying of coatings in a dynamic vacuum guaranteeing the highest quality of gas-thermal coatings. The powders for spraying were produced by the method of mechanical alloying with the use of a planetary mill. As initial components, we used powders of vanadium carbide, ferrochrome, and a cobalt–nickel alloy. We evaluate the corrosion-electrochemical properties of the coatings in a 3% NaCl solution at a temperature of 20 ± 0.2°С and show that they are characterized by high corrosion resistances, which correlates with their porosity. As a result of long-term holding of samples with coatings in a 3% NaCl solution, we observe the penetration of the corrosive medium to the coating–substrate interface, which may lead to underfilm corrosion and exfoliation of the coating. It is shown that a VC–FeCrCo coating whose porosity does not exceed 0.5% obtained by the plasma method in a dynamic vacuum has the lowest corrosion resistance. Its corrosion currents are twice weaker than for the coating obtained by the HVOF method.