Microstructure and corrosion behavior of Yb4Hf3O12 ceramics exposed to air and wet-oxygen at 1400°C

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.