Microstructures and corrosion behavior of HVOF‐sprayed WC‐12%Cr ₃ C ₂ ‐6%Ni coatings before and after sealing

Abstract The WC‐12%Cr ₃ C ₂ ‐6%Ni coatings are prepared by high‐velocity oxygen‐fuel spraying technology on 42CrMo steel substrate, and then the sealing treatment is carried out by sol‐gel aluminum phosphate inorganic sealing agent. The composition, phase structure, morphologies, and porosities of the coatings are characterized by energy dispersive spectrometer (EDS), X‐ray diffraction, scanning electron microscope (SEM), and metallographic gray‐scale methods. Results show that the corrosion current density and corrosion rates of WC‐12%Cr ₃ C ₂ ‐6%Ni coatings in different media are lessened by the aluminum phosphate sealing treatment, which can improve the corrosion resistance of the coating. The corrosion rates of unsealed and sealed coatings immersed in 3.5% Na ₂ SO ₄ solution at 35℃ for 28 days are 0.99 and 0.38 g·m ^–2 ·h ^–1 , and the porosity of the coatings is significantly decreased by the aluminum phosphate sealing treatment, which is lower than 2%. During the immersion corrosion, the sealed and unsealed coatings surface form oxide films with different compositions, which can slow down the corrosion along the normal direction of the coating surface in the process of continuous destruction and regeneration, and no obvious coating/substrate interface corrosion occurs.