Air Plasma-Sprayed Yttria and Yttria-Stabilized Zirconia Thermal Barrier Coatings Subjected to Calcium-Magnesium-Alumino
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Wenshuai Li, Huayu Zhao, Xinghua Zhong, Liang Wang, and Shunyan Tao (Submitted September 4, 2013; in revised form February 27, 2014) Yttria (Y2O3) and zirconia (ZrO2) stabilized by 8 and 20 wt.%Y2O3 thermal barrier coatings (TBCs) subjected to calcium-magnesium-alumino-silicate (CMAS) have been investigated. Free-standing Y2O3, 8 and 20 wt.%YSZ coatings covered with synthetic CMAS slurry were heated at 1300 °C in air for 24 h in order to assess the effect of Y2O3 on the corrosion resistance of the coatings subjected to CMAS. The microstructures and phase compositions of the coatings were characterized by SEM, EDS, XRD, RS, and TEM. TBCs with higher Y2O3 content exhibited better CMAS corrosion resistance. Phase transformation of ZrO2 from tetragonal (t) to monoclinic (m) occurred during the interaction of 8YSZ TBCs and CMAS, due to the depletion of Y2O3 in the coating. Some amounts of original c-ZrO2 still survived in 20YSZ TBCs along with a small amount of m-ZrO2 that appeared after reaction with CMAS. Furthermore, Y2O3 coating was found to be particularly highly effective in resisting the penetration of molten CMAS glass at high temperature (1300 °C). This may be ascribed to the formation of sealing layers composed of Y-apatite phase [based on Ca4Y6 (SiO4)6O and Y4.67(SiO4)3O] by the high-temperature chemical interactions of Y2O3 coating and CMAS glass.
Keywords
CMAS, plasma spraying, thermal barrier coatings, yttria, yttria-stabilized zirconia
1. Introduction Thermal barrier coatings (TBCs) are widely used for thermal protection of hot gas turbines section components (Ref 1-4). Air plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD) are the two most common methods of fabricating TBCs (Ref 5). 8 wt.% yttria-stabilized zirconia (8YSZ) is the typical TBC material used in gas turbines owing to its high-temperature capability, low thermal conductivity, and thermal expansion coefficient which matched well with that of the superalloy substrate (Ref 6). With the increasing operating temperature, several factors of coating degradation coexist. One of the factors is
Wenshuai Li, The Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 201899, China; Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China; and University of Chinese Academy of Sciences, Beijing 100039, China; and Huayu Zhao, Xinghua Zhong, Liang Wang, and Shunyan Tao, The Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 201899, China; and Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China. Contact e-mails: [email protected] and sytao@mail. sic.ac.cn.
Journal of Thermal Spray Technology
related to the stresses induced by the thermally grown oxide (TGO) formed between the bond coat and the YSZ top coat at high temperatures, which accelerates the spalling of TBCs (Ref 7). Another is that caused by particulates in the service environment of gas turbine, which leads to the damage of TBCs by erosi
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