(Ln0.9Gd0.05Yb0.05)2Zr2O7 Ceramics with Pyrochlore Structure as Thermal Barrier Oxides
✍ Scribed by Z.-G. Liu; J.-H. Ouyang; Y. Zhou; J. Li; X.-L. Xia
- Book ID
- 101410359
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 307 KB
- Volume
- 10
- Category
- Article
- ISSN
- 1438-1656
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✦ Synopsis
Ceramic thermal barrier coatings (TBCs) used for thermal insulation against hot combustion gases greatly enhance operating temperatures and thermal efficiency of hot-section components in gas-turbine engines, and reduce fuel consumption and gas emissions at elevated temperatures. [1][2][3] Up to now, the most successful TBC materials in use are 7 ± 1 wt.%Y 2 O 3 stabilized ZrO 2 (7YSZ). However, 7YSZ is limited to operate below 1200 °C. Above 1200 °C, the t'-phase zirconia transforms into tetragonal and cubic phases. During cooling the tetragonal phase will further transform into monoclinic phase, which is accompanied with a volume change of 3-5 % and invariably causes cracking and failure. The relatively porous 7YSZ plasma-sprayed coatings are prone to sintering above 1200 °C, which increases thermal conductivity and makes them less effective. To further improve the thermal insulation properties, it is urgently needed to develop new thermal barrier oxide materials with a lower thermal conductivity than 7YSZ. Some important requirements for excellent TBC materials are high melting point, high phase stability, low thermal conductivity, chemical inertness, high thermal expansion coefficient, high strain tolerance and low sintering rate at elevated temperatures. [4] Among high-melting temperature ceramic materials, rareearth zirconates, with the general formula Ln 2 Zr 2 O 7 (Ln = La, Nd, Sm, Eu, Gd, etc), have a distinctly lower thermal conductivity than 7YSZ. [5,6] Pyrochlore-structured La 2 Zr 2 O 7 -based TBCs were successfully prepared with electron beam physical vapor deposition (EB-PVD) method by Saruhan et al. [7] The hot corrosion resistance of La 2 Zr 2 O 7 coatings was better than that of 8 wt.% yttria-stabilized zirconia coatings produced by thermal spraying, and La 2 Zr 2 O 7 coatings remained well