Development of protective coating for X8CrNiMoVNb16-13 alloy in high-temperature molten salt environment through high-velocity oxy-fuel sprayed NiCrMoNb and Cr₃C₂-25NiCr powder coating

Abstract

Various industries extensively use the high-velocity oxy-fuel coating technique due to its superior quality, cost-effectiveness, flexibility and convenience for use. The present research distinguishes the high-temperature corrosion characteristics of high-velocity oxy-fuel coated NiCrMoNb and Cr3C2-25NiCr powder on X8CrNiMoVNb16-13 alloy. The oxidation and hot corrosion characteristics of X8CrNiMoVNb16-13 alloy were evaluated through the air and molten salt condition (60% V2O5 + 40% Na2SO4) for 50 cycles at a temperature of 900°C. Thermogravimetric measurement was performed to evaluate the weight gain square of coated and uncoated substrates. Vickers hardness, thickness, porosity and microstructure of the coating were analysed. The metallurgical integrity of the corrosion product is evaluated through scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. The laminar structure was observed in the coated region. Also, the dense microstructure with maximum porosity of 0.66% was observed, and the thickness of both the coatings was similar. The Cr3C2-25NiCr coating (766 ± 11 HV0.3) showed higher Vickers hardness than NiCrMoNb (377 ± 10 HV0.3). The occurrence of Cr2O3, NiFe2O4 and NiCr2O4 increased the corrosion resistance in both molten salts and air oxidation environments. The development of Fe2O3 in NiCrMoNb coating increases the weight gain when exposed to the molten salt condition. The present research recommended that Cr3C2-25NiCr coating can be used for the molten salt condition, whereas NiCrMoNb can be used for air oxidation application.