Corrosion behavior of HVOF sprayed Cr₃C₂-NiCr coating in 3.5%NaCl solution

FeNiBSi/Cr₃C₂ composite coating was deposited on 45 steel by high velocity arc spay process. Microstructure of the coating was analyzed by optical microscopy and scanning election microscopy(SEM). Phases were identified by X-ray diffraction(XRD) analysis. Hot corrosion behavior of the coating was tested under a mixed molten salt of Na₂SO₄+K₂SO₄(7DK(:DK)3) at 550-750℃ for 100 h. The results showed that the coating has a typical lamellar structure. Corrosion kinetic curves of the coating at different temperatures approximatively follow the parabolic law. It was clear that the hot corrosion resistance of the coating is much more excellent than that of 20G steel. At 550 and 650℃, the high corrosion resistance is mainly due to the formation of a protective oxide layer which is composed of Fe₂O₃, Cr₂O₃ and FeCr₂O₄. The oxide film is imperfect at 750℃ which cannot effectively block the molten salts. So the hot corrosion resistance is poor at 750℃.