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 O2 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)6O2, resulting in rapid crystallization of CMAS