High-Temperature Chemical Stability of Hf6Ta2O17 Ceramic for Thermal Barrier Coatings

High-temperature chemical stabilities of Hf6Ta2O17/Al2O3, Hf6Ta2O17/YSZ and Hf6Ta2O17/Sm2Zr2O7 were studied for thermal barrier coatings (TBCs). The mixed powders of Hf6Ta2O17/Al2O3 and Hf6Ta2O17/YSZ were annealed at 1600 degrees C for 8 hours in air, and the mixed powders of Hf6Ta2O17/Sm2Zr2O7 were annealed at 1200 degrees C for 8 hours in air. The phases of the mixed powders after annealed were observed by X-ray diffractometry (XRD). The sample of Hf6Ta2O17/Al2O3 mixed powder was molded and sintered at 1600 degrees C for 8 hours in air, and the microstructures of the sintered sample were investigated by scanning electron microscopy (SEM). The XRD results revealed that the crystal structure of Hf6Ta2O17 had no remarkable changes in the mixed powders of Hf6Ta2O17/YSZ and it had changes in the mixed powders of Hf6Ta2O17/Al2O3. The monocline HfO2/ZrO2 phases were found in the mixed powders of Hf6Ta2O17/Sm2Zr2O7. The SEM results showed that the boundaries of Hf6Ta2O17 and Al2O3 crystals were clear. The element composes in crystals were analyzed by energy dispersive spectrometer (EDS), and the EDS results showed that a little amount of Al diffused into Hf6Ta2O17 crystals.