Abstract: As the operating temperature of aero-engine rises, the degradation of thermal barrier coatings and environmental barrier coatings on hot-section components due to the infiltration of calcium-magnesium-alumina-silicate (CMAS) has garnered increasing attention. Rare earth constituents play an essential role in the formation of corrosion products and the subsequent melt penetration when conventional thermal barrier coatings and environmental barrier coatings are attacked by CMAS deposits. This study focused on the preparation of a series of gadolinium-ytterbium oxides ((Gd_xYb_1-x)₂O₃, x = 0, 0.05, 0.10, 0.20, 0.30, 0.50 and 1.00), with particular emphasis on the roles of ytterbium and gadolinium, which were commonly utilized in thermal barrier coatings and environmental barrier coatings. Their reaction with CMAS deposits was systematically investigated at 1300 ^oC to explore the synergistic mechanism associated with these two rare earth elements. The results indicate that gadolinium cations can efficiently induce the crystallization of products with apatite structure which have a low melt consumption. Conversely, ytterbium cations can induce the formation of products with garnet and silicocarnotite structure which have a sluggish kinetic. Furthermore, the partitioning of gadolinium and ytterbium ions within corrosion products, along with variation of residual CMAS melt composition, was further discussed. It is proposed that these two rare earth ions exhibit a synergistic effect within a certain composition range (5%-20% of gadolinium content(in mol)). The optimized ratio of gadolinium and ytterbium within coatings is anticipated to promote apatite crystallization, prevent melt penetration, and modify the sluggish crystallization kinetic of garnet and silicocarnotite, thereby significantly improving the melt consumption. The investigation on synergistic effect of gadolinium and ytterbium cations provides theoretical support for the anti-CMAS-corrosion composition modification of thermal and/or environmental barrier coating.

Key words: Gadolinium-ytterbium oxides, CMAS corrosion, reactive crystallization products, synergistic effect