Study on Microstructure and Thermal Cycling Performance of the Plasma-sprayed YSZ Coating in Simulated Turbine Environment

Abstract

To enhance the efficiency and durability of the gas turbine and aircraft components, thermal barrier coatings (TBCs) are the most considerable protection techniques available. The present work is mainly concentrating on improving the high-temperature corrosion characteristics of uncoated and plasma-spray coated alloy A-286 under Na₂SO₄-5%NaCl-7.5%NaVO₃ deposit at 900°C. By using plasma spray process NiCrAlY and YSZ (bond coat-NiCrAlY and top coat-YSZ) thermal barrier coating was deposited on the alloy A-286. Coating characterization such as roughness was analysed on the coating surface and coating thickness and hardness analysis were performed on the coating region at the cross section. X-ray diffraction (XRD) and scanning electron microscope (SEM) were employed to study the phases and coating microstructure before and after being subjected to corrosion. The rate of corrosion was derived by thermo-gravimetric analysis. Using the elemental mapping technique and EDS compositional analysis, the scale thickness and corrosion attack were identified. During the corrosion experiment, sputtering and spallation of oxide were noticed on the uncoated specimen. The oxide layer failure was not found in both the coated specimens. The results indicated that YSZ coating exhibits a better corrosion resistance than NiCrAlY. The reaction products such as monoclinic ZrO₂ and YVO₄ were found in the corroded YSZ coating. There was no significant failure, but degradation was found on the coating due to molten salt.