Evaluation of a sealed layer on a porous thermal barrier coating against molten calcium-magnesium-alumina-silicate corrosion

Thermal barrier coatings (TBCs) can improve the high-temperature performance of turbine blades, however, the complex service environment such as Ca-Mg-Al-silicate (CMAS) is the main reason for the coating failure. The corrosive medium (Ca2+ and Si4+) penetrates the TBCs through the porous structure combined with surface defects. In this study, three different sealed layers (Zr, Al, and Al-Y) were deposited on the traditional TBCs by using magnetron sputtering. The cross-sectional morphologies showed the continuous structure of the sealed layer improved the pore filling effect. When O-2 is adsorbed at the top position of the Al atom, the lowest adsorption energy of the YAl3 (0001) surface is -5.34 eV which can provide stronger chemical adsorption energies for Al and O. The Al-Y sealed layer was preferred to form an aluminum oxide film. The experimental results of CMAS corrosion showed that Al-Y sealed layer can achieve long-lasting protection because the aluminum yttrium oxide (Al2Y4O9) reacts with CaO and SiO2 at the interface and finally formed Ca3Y2(SiO4)(6)O-2, resulting in rapid crystallization of CMAS. (C) 2021 The Authors. Published by Elsevier Ltd.