High Temperature Corrosion Performance of HVOF and D-gun Formulated Cr₃C₂-NiCr and Rare Earth Element Doped Cr₃C₂-NiCr Coating on TP347H Austenite Steel

The present research evaluates the microstructure and hot corrosion performance of HVOF and D-gun sprayed Cr₃C₂-25NiCr, and ceria (0.4 wt.%) blended Cr₃C₂-25NiCr coatings on TP347H superheater tube material. All the specimens were subjected to Na₂SO₄-60%V₂O₅ environment for 50 cycles at 900 °C. The corroded samples were evaluated using thermogravimetric analysis, XRD, scanning electron microscopy with energy dispersive spectroscopy, and x-ray mapping. Moreover, the weight gain versus oxidation time and oxide scale growth rate was subsequently examined. Microstructural results revealed that the ceria-added coating with the D-gun method provided better coating features, such as microhardness, surface roughness, and microporosity than its counterparts. Among the four coatings, D-gun sprayed Ce 0.4 wt.% added Cr₃C₂-25NiCr coating (D2) proved to be better due to the thin and dense oxide scale of Cr₂O₃, Cr₂₃C₆, NiCr₂O₄, Ce₂O₃, and CeVO₄. Moreover, the presence of ceria in the carbide coating reduces the development of the NiCr₂O₄ phase resulting in compact oxide scale of Cr₂O₃ developed on the coating surface.