Abstract:

Rare earth silicate environmental barrier coatings (EBCs) are important materials that can be applied to hot sections for the new generation of high thrust-to-weight ratio aero engines. However, oxidation and cracking of the silicon bond layer are significant factors leading to failure during service. Modifying the silicon bond layer has become an important method to extend EBCs’ service life. In this work, Yb₂O₃ was doped in the silicon bond layer to mitigate cracking under high-temperature water vapor conditions, as well as to improve its corrosion resistance. Five kinds of EBC systems (Si-Yb₂O₃)/Yb₂Si₂O₇/Yb₂SiO₅ with different Yb₂O₃ doping (0, 5%, 10%, 15%, 20%, in volume) were prepared on SiC substrates using vacuum plasma spraying technology. Their water-oxygen corrosion behavior was studied, and mechanisms at 1350 ℃ beneath their behavior were revealed. The results indicated that doping an appropriate amount (5%) of Yb₂O₃ into silicon effectively facilitates the reaction with SiO₂ and its subsequent consumption during high-temperature water vapor corrosion. This process reduces the stress variations associated with SiO₂ phase transition (β → α) and inhibits formation of longitudinal cracks in mixed thermal growth oxide (mTGO) layer, thus enhancing structural stability. Furthermore, the reaction product of Yb₂Si₂O₇ exhibits a suitable coefficient of thermal expansion (CTE) and chemical compatibility. Notably, increasing Yb₂O₃ content results in formation of interconnected "skeleton" structure within the bond layer, which may provide a direct pathway for oxidizing substances to permeate into the interior of coating, thereby facilitating corrosion process within the bond layer, and ultimately diminishing the water vapor corrosion resistance of EBC systems.

Key words: environmental barrier coating, water vapor corrosion, modified bond layer, vacuum plasma spray