STABILIZATION AND CORROSION RESISTANCE UNDER HIGH-TEMPERATURE OF NANOSTRUCTURED CeO2/ZrO2-Y2O3 THERMAL BARRIER COATING

Thermal barrier coating (TBC) systems are being used in thermal insulation components in the hot sections of gas turbines in order to increase operation temperature with better efficiency. The typical material of TBC is yttria stabilized zirconia (YSZ) because of its high thermal expansion coefficient, which closely matches that of the substrate, and low thermal conductivity. However, YSZ based TBC systems cannot be successfully applied due to hot corrosion problems caused by molten salts, such as Na, S and V, contained in low quality fuels. In recent years, nanostructured TBC attracted intense attentions due to their enhanced thermal physical properties, but the thermal stability and resistance to molten salt performance are rarely studied. As a new candidate TBC material, ceria and yttria stabilized zirconia currently looks to be promising. The purpose of this work was to obtain the better understanding of microstructure and molten salt corrosion capability of plasma-sprayed nanostructured CSZ coating and to provide some foundation for improving the properties of TBC. In this work, nano-sized ZrO2-8%Y2O3 (YSZ, mass fraction) and nano-YSZ doped with 25% of nanometer CeO2 (CeO2/ZrO2-8%Y2O3, CSZ) were deposited on GH30 superalloy surface through air plasma spray process (APS) to form a thermal barrier coating. The morphology and microstructure of the CSZ coating were characterized using FESEM and XRD. The grain size of CSZ coating under the following two conditions were examined, firstly, the CSZ coating was heated to 1100 degrees C and held for various durations, then the CSZ coating was heated for a fixed 10 h but up to various temperatures. Its corrosion resistance under high temperature molten Na2SO4 salt was also tested. The results showed that average grain size of CSZ coating grown from 45 to 63 nm under prolonged exposure to high temperature and CSZ has showed better corrosion resistance than YSZ coating with no m-ZrO2 phase precipitated at under prolonged high temperature at 900 degrees C in Na2SO4 salt corrosion.