High velocity oxygen fuel sprayed Cr3C2-NiCr coatings against Na2SO4 hot corrosion at different temperatures

Cr3C2-NiCr/NiCrAlY coating was prepared by high velocity oxygen fuel (HVOF) spraying. The microstructure and the Na2SO4 hot corrosion behavior at different temperatures of the coating were investigated. The Na2SO4 hot corrosion mechanism of Cr3C2-NiCr coating was also discussed. The results showed that HVOF Cr3C2-NiCr coating was relatively dense and mainly composed of Cr3C2, NiCr and a small amount of Cr7C3 three phases. The dense Cr2O3 layer was formed on the surface of Cr3C2-NiCr coating after Na2SO4 corrosion at 750 degrees C to further prevent corrosion. The coating had produced the obvious longitudinal crack with the increase of hot corrosion temperature up to 900 degrees C. The corrosion mechanism of Cr3C2-NiCr coating against the Na2SO4 salt at high temperature was as follows: firstly, the protective oxidizing film was formed at 750 degrees C, then the protective oxide film dissolved at the interface between the coating and Na2SO4 salt with the hot corrosion temperature increasing up to 900 degrees C, and subsequently the dissolved anions and cations could migrate to the interface between molten salt and air and the loose and unprotected oxides were regenerated, thereby exacerbating the failure of the coating.