Effect of chromium on hot corrosion behavior of arc-sprayed NiCr coatings

In this article, NiCr coatings with chromium content of 13%, 27% and 41% were prepared by arc spraying. They were exposed in molten salts (NaCl-Na₂SO₄) at 800 ℃ for 200 hours. The effect of chromium content on the hot corrosion behavior of the coatings was investigated. X-ray diffraction (XRD) and scanning electron microscope with energy dispersion spectrum (SEM-EDS) were used to analyze the phase compositions, morphologies and chemical compositions of the coatings. The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content, which resulted in NiO being the major reaction product. It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating. The basic fluxing of Cr₂O₃ lowered its protection during the hot corrosion process and led to the formation of porous Cr₂O₃ on the NiCr41 coating. The molten salts accelerated the oxidation reaction resulting in thicker and porous oxide scales formed on the surfaces of coatings.