Ultrafast high-temperature sintering of Ta-doped high-entropy fluorite ceramics with dual physical-chemical mitigation against CMAS corrosion

Traditional yttria-stabilized zirconia and conventional high-entropy fluorite oxides (HEOs) are crucial materials as thermal barrier coatings (TBCs) in high-temperature engineering applications. However, corrosive deposits of molten calcium-magnesium-alumino-silicate (CMAS) on the surface induce severe thermochemical degradation, thereby severely deteriorating the structural integrity and thermal efficiency of the coating system. To enhance the CMAS corrosion resistance of HEOs, this study introduces a novel doping strategy that utilizes the ultrafast high-temperature sintering (UHS) method to co-incorporate tantalum (Ta 5 + ) and multi-principal rare-earth (RE) ions into the fluorite-structured HEO matrix. The UHS method enables rapid preparation of Ta-doped HEO within 60 s, while maintaining the single-phase fluorite structure. The doping of Ta 5+ ions significantly enhances the reaction with Si and Ca elements in the CMAS melt, thereby promoting the crystallization of CaTa 2 O 6 , Ca 2 Al 2 SiO 7 , and MgAl 2 O 4 phases, while the formed CaTa 2 O 6 particles serve as heterogeneous nucleation substrates for anorthite precipitation. Concurrently, the participation of multiple RE ions in the precipitation of Ca 2 RE 8 (SiO 4 ) 6 O 2 and separated RE-MeO 2−δ phase consolidates with the CaTa 2 O 6 phase to form a dense multiphase composite layer at the interface, effectively hindering the diffusion of CMAS melt through both physical blocking and chemical inhibition. Ultimately, this study provides a practical basis for designing the next generation of corrosion-resistant TBC materials capable of withstanding extreme environments. Download: Download high-res image (265KB) Download: Download full-size image In this work, the dense Ta 5+ -doped HEOs were successfully fabricated by the UHS method. After following prolonged corrosion in molten CMAS salts at 1300 °C, the significant phase separation occurred in the undoped HEO ceramic, while a substantial reaction interface layer on the surface of the HEO ceramic. Meanwhile, a compact surface layer comprising apatite and phase-separated fluorite phases formed, effectively blocking further CMAS penetration. It is worth noting that the corroded 0.2Ta-doped HEO after the CMAS corrosion reaction generates enriched Ta 5+ and RE ions in the CMAS melt. This increased the reaction with Si and Ca element at high temperatures, promoting substantial crystallization of the CaTa 2 O 6 , Ca 2 Al 2 SiO 7 , and MgAl 2 O 4 phases. Meanwhile, the interface layer formed a densely structured surface composed primarily of apatite, secondary fluorite phases, and CaTa 2 O 6 particles. When the temperature was elevated to 1500 °C, the atomic mobility within CMAS increased, and the growth rate of the interfacial reaction layer formed by 0.2Ta-doped HEO significantly reduced, demonstrating that the compact reaction layer retains its ability to inhibit CMAS corrosion even at elevated temperatures. Fig. The synthesis route and anti-CMAS corrosion behavior of the HEOs