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

Subscript text High-temperature chemical stabilities of Hf 6 Ta 2 O 17 /Al 2 O 3 , Hf 6 Ta 2 O 17 /YSZ and Hf 6 Ta 2 O 17 /Sm 2 Zr 2 O 7 were studied for thermal barrier coatings (TBCs). The mixed powders of Hf 6 Ta 2 O 17 /Al 2 O 3 and Hf 6 Ta 2 O 17 /YSZ were annealed at 1600°C for 8 hours in air, and the mixed powders of Hf 6 Ta 2 O 17 /Sm 2 Zr 2 O 7 were annealed at 1200°C for 8 hours in air. The phases of the annealed mixed powders were observed by X-ray diffractometry (XRD). The sample of Hf 6 Ta 2 O 17 /Al 2 O 3 mixed powder was molded and sintered at 1600°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 Hf 6 Ta 2 O 17 had no remarkable changes in the mixed powders of Hf 6 Ta 2 O 17 /YSZ and it had changes in the mixed powders of Hf 6 Ta 2 O 17 /Al 2 O 3 . The monocline HfO 2 /ZrO 2 phases were found in the mixed powders of Hf 6 Ta 2 O 17 /Sm 2 Zr 2 O 7 . The SEM results showed that the boundaries of Hf 6 Ta 2 O 17 and Al 2 O 3 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 Hf 6 Ta 2 O 17 crystals.