Design of Ti <sub>2</sub>AlC/YSZ TBCs for more efficient in resisting CMAS attack
Lei Guo, Yanyan Li, Guang Li
Abstract
Ti<sub>2</sub>AlC has been demonstrated as a promising protective layer material for thermal barrier coatings (TBCs) against calcium-magnesium-alumina-silicate (CMAS) attack. In this study, the reliability of Ti<sub>2</sub>AlC coatings against CMAS corrosion was explored, and new Ti<sub>2</sub>AlC/YSZ TBCs more efficiently resistant to CMAS were designed. The fabricated Ti<sub>2</sub>AlC coatings inevitably contain some impurity phases (TiC and Al<sub>2</sub>Ti<sub>3</sub>), the contents of which were minimized by optimizing the spraying distance. Corrosion tests revealed that Ti<sub>2</sub>AlC/YSZ TBCs yielded higher resistance to CMAS attack than YSZ TBCs, but with long-term exposure to CMAS, the Ti<sub>2</sub>AlC protective coating exhibited microstructure degradation due to the presence of impurity phases, which caused the formation of a layer mixed with Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> rather than a continuous compact Al<sub>2</sub>O<sub>3</sub> layer on the surface. Pre-oxidation schemes were designed in air or with a controlled oxygen partial pressure, which revealed that pre-oxidation at an oxygen partial pressure of ~ 630 Pa could promote a continuous Al<sub>2</sub>O<sub>3</sub> layer is formed on the Ti<sub>2</sub>AlC protective coating surface. Furthermore, vacuum heat treatment at 867 ℃ for 10 h before pre-oxidation was beneficial for the formation of the compact Al<sub>2</sub>O<sub>3</sub> layer. Through the above scheme design, new Ti<sub>2</sub>AlC/YSZ TBCs were obtained, which had reduced impurity phase contents and a pre-oxide layer with an ideal structure on the surface. The new TBCs exhibit higher microstructure stability exposed to CMAS and more efficient CMAS resistance.