Unraveling the effect of water content in the electrolyte on the microstructure and oxidation performance of anodized Ti45Al8.5Nb alloy

TiAl alloys are promising materials for high-temperature applications due to their lightweight and superior mechanical properties, but their oxidation resistance significantly deteriorates above 700°C. Anodization in fluorine electrolyte has emerged as an effective strategy to address this challenge. In this study, we systematically investigated the role of water content in NH₄F/ethylene glycol electrolyte on the microstructure and oxidation performance of anodized Ti45Al8.5Nb alloy. Results revealed that water content critically influences the oxygen source and fluoride enrichment in the anodic film. Anodization in anhydrous electrolyte results in the formation of a mixture loose oxide scale due to the volatilization of organic component from the anodic film and elevated oxygen partial pressure at the anodic film/substrate interface. In contrast, introducing 2% water promotes the development of a compact Al₂O₃-based oxide scale. After 100 h oxidation at 1000 °C, the weight gain of Ti45Al8.5Nb alloy anodized in the electrolyte with optimal water content was less than half of the sample anodized in anhydrous electrolyte.