Design of Ti₂AlC/YSZ TBCs for more efficient in resisting CMAS attack

Ti₂AlC has been demonstrated as the promising protective layer material for thermal barrier coatings (TBCs) against calcium–magnesium–alumina–silicate (CMAS) attack. In this study, the reliability of Ti₂AlC coatings against the CMAS corrosion was explored, and new Ti₂AlC/YSZ TBCs more efficiently resistant to CMAS were designed. The fabricated Ti₂AlC coatings inevitably contain some impurity phases (TiC and Al₂Ti₃), the contents of which were minimized by optimizing the spraying distance. Corrosion tests revealed that Ti₂AlC/YSZ TBCs yielded higher resistance to the CMAS attack than YSZ TBCs, but with long-term exposure to CMAS, the Ti₂AlC protective coating exhibited microstructure degradation due to the presence of the impurity phases, which caused the formation of a layer mixed with Al₂O₃ and TiO₂ rather than a continuous compact Al₂O₃ layer on the surface. Pre-oxidation schemes were designed in air or with a controlled oxygen partial pressure, which revealed that the pre-oxidation at an oxygen partial pressure of ~630 Pa could promote a continuous Al₂O₃ layer formed on the Ti₂AlC protective coating surface. Furthermore, a vacuum heat treatment at 867 ℃ for 10 h before pre-oxidation was beneficial for the formation of the compact Al₂O₃ layer. Through the above scheme design, new Ti₂AlC/YSZ TBCs were obtained, which had reduced impurity phase contents and a pre-oxide layer with an ideal structure on the surface. New TBCs exhibit higher microstructure stability exposed to CMAS and more efficient CMAS resistance.