Abstract
This research article discusses in detail how the rate of corrosion increases for the Alloy 254 in the molten salt mixture of 10 wt% NaCl + 40 wt% K2SO4 + 40 wt% Na2SO4 + 10 wt% KCl and corrosive gas combination of 2.5% SO2 + 3% O2 + 25% CO2 + 69.5% N2 in simulated municipal solid waste incinerator environment at 700 °C and 800 °C. In addition, the article shows rate of thermal corrosion abridged due to the addition of 80 Ni- 20 Cr -High-velocity oxygen fuel coating on the SMO 254 specimen. Thermogravimetric analysis is adapted to analyze the corrosion rate. A higher hardness was obtained for the High-velocity oxygen fuel coated specimen than that of base metal. Surface roughness was measured on the thermal barrier coated surface. As a result of the impact of molten salt and corrosive gas, hot corrosion by-products such as sulphides, chlorides and Na are produced, which are observed to increase the severity of corrosion rate. The study provides a detailed analysis of the metallurgical changes along the cross-section on the hot corroded samples by optical and Scanning electron microstructural image analysis. X-ray diffraction analysis was used to know about the corrosion products formed during corrosion. Formation of the major protective oxide phases such as NiCr2O4, Cr2O3, NiO and CrMnO4 provide better corrosion resistance to the substrate in the coated samples. The diffusion of the corrosive elements along the cross-section of the weld interface, weld zone, and base metal zone was analyzed in detail using Electron dispersive spectroscopy data in the point scan, line scan, and x-ray mapping techniques. Thermal spray coatings were found to be effective to prevent the hot corrosion, however, a higher weight gain (17.75 mg cm−2) was observed on the pulse current gas tungsten arc weldment sample in the simulated environment compared to a weight gain (2.66 mg cm−2) base metal specimen at 700 °C. Spallation of coated surface occurred at 800 °C, and it could be concluded that the coating has found to be effective in preventing the hot corrosion and safe to operate at a temperature of 700 °C for Alloy 254 in this aggressive simulated environment.
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