Microstructure and corrosion behavior of Yb ₄ Hf ₃ O ₁₂ ceramics exposed to air and wet‐oxygen at 1400°C

Abstract Rare‐earth hafnates show promising potential use in the development of a new generation of thermal/environmental barrier coatings (T/EBCs) owing to their high melting point, phase stability, and compatibility with SiC‐based composites. In the current work, microstructural evolution and corrosion behavior of Yb ₄ Hf ₃ O ₁₂ ceramics exposed to wet‐oxygen and ambient air atmospheres at 1400°C were systematically investigated. Results revealed that sintering in air led to pronounced grain growth and homogenization, followed by secondary recrystallization at extended durations. Under wet‐oxygen conditions, the ceramics underwent two distinct stages: initial Hf ^{4 +} hydration and volatilization (0–20 h), and subsequent formation of Al ₅ Yb ₃ O ₁₂ corrosion products due to reactions with Al(OH) ₃ impurities (20–40 h). These processes induced fluctuations in grain size distribution, including growth, refinement, and re‐coarsening, accompanied by microstructural densification and grain boundary corrosion. The findings highlight the pronounced role of water vapor and trace environmental impurities, demonstrating that alumina‐based furnace environments can act as a variable influencing the structural integrity and apparent degradation behavior of Yb ₄ Hf ₃ O ₁₂ , thereby providing valuable guidance for mechanistic studies of high temperature corrosion in future experimental investigations.