Comparative study of water vapor corrosion resistance in directionally solidified RE3Al5O12/Al2O3 eutectic ceramics at 1500℃: Effect of eutectic structure and rare earth elements

Al 2 O 3 -based directionally solidified eutectic (DSE) ceramics are recognized as promising candidates for high-temperature structural materials in advanced aeroengines. Nevertheless, their corrosion resistance at elevated temperatures continues to pose a critical challenge, limiting broader application in hot-section components. This study investigates corrosion behavior of RE 3 Al 5 O 12 (REAG)/Al 2 O 3 (RE = rare earth) DSE ceramics in water vapor atmosphere (90 vol.% H 2 O(g) + 10 vol.% air(g)) at 1500℃ for durations up to 200 hours, with focus on the influence of eutectic structure and RE elements in garnet phases via examining three samples (high-entropy (Y 0.2 Gd 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 DSEs fabricated at 10 and 300 mm/h and YAG/Al 2 O 3 DSE grown at 10 mm/h). The results indicate that REAG/Al 2 O 3 DSE ceramics exhibit excellent water vapor corrosion resistance at 1500°C for up to 200 hours, with mass loss values ranging from -0.00757 to -0.00708 mg·cm -2 ·mg -1 . During corrosion, Al 2 O 3 phase acts as corrosion-susceptible component compared to REAG phase, with corrosion depth showing a nearly linear relationship with the average Al 2 O 3 lamellar width. In addition, garnet phases experience slight grain growth, reducing the contact area between water vapor and Al 2 O 3 phase; Gd demonstrates marginally lower stability compared to other RE elements. Despite these changes, all samples maintain their preferred crystallographic orientations, confirming the structural stability of REAG/Al 2 O 3 DSEs under water vapor atmosphere at 1500℃. • RE 3 Al 3 O 12 /Al 2 O 3 eutectic ceramics exhibit superior water vapor corrosion resistance in 90 vol.% H 2 O-10 vol.% air at 1500℃ for 200 h, with mass losses of --0.00757 to -0.00708 mg·cm -2 ·mg -1 . • RE 3 Al 3 O 12 exhibited enhanced corrosion resistance over Al 2 O 3 , which contributed predominantly to the mass loss and strongly correlated with the widths of Al 2 O 3 lamellar. • The RE 3 Al 3 O 12 phase demonstrated exceptional stability during corrosion, with its preferred crystallographic orientation remaining unchanged after water vapor corrosion.