Abstract:The corrosion resistance characteristics of RE-rich RE₅₀Ta_xZr_50-xO_175+0.5x oxides in RE₂Zr₂O₇-RETaO₄ systems to calcium-magnesium-alumino-silicate (CMAS) at 1300 °C, and the influence of RE³⁺ and Ta⁵⁺ on chemical reactions and reactive crystallization of CMAS melts were investigated. The results show that following the thermochemical reactions, apatite, pyrochlore, reprecipitated fluorite and residual Yb(Y)TaO₄ phases were the predominant reaction products. Formation abilities of apatite and pyrochlore were found to be proportional to the ionic radius of RE³⁺. The increase of Ta⁵⁺ amount can decrease the number of available RE³⁺ to form apatite. Moreover, the resistance characteristic to CMAS corrosion in RE₅₀Ta_xZr_50-xO_175+0.5x systems was decided by the combined action of apatite and pyrochlore phases. The cohesive mixture of apatite and pyrochlore phases can generate a dense layer near the reaction front, which had a positive effect on suppressing CMAS infiltration. The ability of the fluorite + RETaO₄ two-phase field was determined to be sufficient to mitigate CMAS corrosion.

Key words: thermal barrier coatings; CMAS corrosion; thermochemical reaction; apatite; pyrochlore; penetration experiment