Abstract
Three types of thermal barrier coatings, namely NiCrAlY/YSZ double-layer, NiCrAlY/YSZ/mullite three-layer and NiCrAlY/YSZ/gradient of YSZ and mullite coatings, were deposited on a nickel-base superalloy using a plasma spray method. Hot corrosion studies of the plasma-sprayed thermal barrier coatings were conducted in 45wt% Na2SO4 + 55 wt% V2O5 molten salt at 1050 °C. Microstructure and morphology of the coatings were examined and compared by scanning electron microscopy and X-ray diffraction. The addition of mullite in thermal barrier coating results in the mullite phase reacting with corrosive salt and oxygen to form NaAlSiO4 phase. In addition to this phase, alumina (Al2O3) and Na2O phases are also formed. The presence of alumina phase (Al2O3) along with Na2O leads to formation of NaAlO2. A dense layer of NaAlO2 can increase the resistance to hot corrosion of the coating compared to YSZ coating.
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