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

Abstract

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.

Keywords

• thermal barrier coatings (tbcs)
• calcium–magnesium–alumina–silicate (cmas)
• ti₂alc/ysz
• pre-oxidation design
• corrosion resistance mechanisms