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Title: Effect of CMAS composition on hot corrosion behavior of gadolinium zirconate thermal barrier coating materials

Abstract

The resistance of synthesized pyrochlore-type Gd 2Zr 2O 7 bulk specimens to four calcium-magnesium aluminosilicate (CMAS) compositions at different temperatures was investigated. The reaction products were identified by x-ray diffraction and penetration depths were examined using scanning electron microscopy. A dense reaction layer is comprised mainly of Ca 2Gd 8(SiO 4) 6O 2 and a cubic fluorite phase formed during the CMAS attack, and some unreacted CMAS was found in a transition layer below the reaction layer. The overall infiltration depth changed slightly with temperature, however, the thickness of the reaction layer and the morphology of the transition layer varied distinctly with temperature. The sintered sample underwent the most severe degradation by the CaO-lean CMAS, whereas the effect of CaSO 4 and CaCO 3 was not significant. Furthermore, the Gd content of the ZrO 2-based cubic fluorite phase depends on the temperature and the molar ratio of Ca:Si in the CMAS.

Authors:
 [1];  [1]
  1. Auburn Univ., Auburn, AL (United States)
Publication Date:
Research Org.:
Auburn Univ., AL (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE), Clean Coal and Carbon (FE-20)
OSTI Identifier:
1372487
Grant/Contract Number:
FE0011245
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Volume: 164; Journal Issue: 9; Journal ID: ISSN 0013-4651
Publisher:
The Electrochemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CMAS; fluorite; Gd2Zr2O7; pyrochlore; thermal barrier coatings

Citation Formats

Deng, Wenzhuo, and Fergus, Jeffrey W. Effect of CMAS composition on hot corrosion behavior of gadolinium zirconate thermal barrier coating materials. United States: N. p., 2017. Web. doi:10.1149/2.0531709jes.
Deng, Wenzhuo, & Fergus, Jeffrey W. Effect of CMAS composition on hot corrosion behavior of gadolinium zirconate thermal barrier coating materials. United States. doi:10.1149/2.0531709jes.
Deng, Wenzhuo, and Fergus, Jeffrey W. 2017. "Effect of CMAS composition on hot corrosion behavior of gadolinium zirconate thermal barrier coating materials". United States. doi:10.1149/2.0531709jes. https://www.osti.gov/servlets/purl/1372487.
@article{osti_1372487,
title = {Effect of CMAS composition on hot corrosion behavior of gadolinium zirconate thermal barrier coating materials},
author = {Deng, Wenzhuo and Fergus, Jeffrey W.},
abstractNote = {The resistance of synthesized pyrochlore-type Gd2Zr2O7 bulk specimens to four calcium-magnesium aluminosilicate (CMAS) compositions at different temperatures was investigated. The reaction products were identified by x-ray diffraction and penetration depths were examined using scanning electron microscopy. A dense reaction layer is comprised mainly of Ca2Gd8(SiO4)6O2 and a cubic fluorite phase formed during the CMAS attack, and some unreacted CMAS was found in a transition layer below the reaction layer. The overall infiltration depth changed slightly with temperature, however, the thickness of the reaction layer and the morphology of the transition layer varied distinctly with temperature. The sintered sample underwent the most severe degradation by the CaO-lean CMAS, whereas the effect of CaSO4 and CaCO3 was not significant. Furthermore, the Gd content of the ZrO2-based cubic fluorite phase depends on the temperature and the molar ratio of Ca:Si in the CMAS.},
doi = {10.1149/2.0531709jes},
journal = {Journal of the Electrochemical Society},
number = 9,
volume = 164,
place = {United States},
year = 2017,
month = 7
}

Journal Article:
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  • Zirconium oxide or zirconia (ZrO{sub 2})-based thermal barrier coatings (TBC) and aluminum oxide (Al{sub 2}O{sub 3}) layers were fabricated by detonation gun (D-gun) spraying. Al{sub 2}O{sub 3} layers with thicknesses of 50 {micro}m, 150 {micro}m, or 250 {micro}m were applied to a duplex TBC system as an intermediate layer or a surface layer, and their effects on the oxidation behavior of the TBC coatings were investigated at 1,200 C. Oxidation kinetics showed that the suitable application of Al{sub 2}O{sub 3} layers suppressed the oxidation of the Ni-Cr-Al-Y bond coat, and the oxidized rates were partially dependent on the thickness ofmore » the Al{sub 2}O{sub 3} layers. In the case of an Al{sub 2}O{sub 3} layer applied onto the surface, the durability and integrity of the TBC coatings were improved remarkably and the oxidation resistance was enhanced. However, a deteriorating spallation occurred for the specimens with an Al{sub 2}O{sub 3} intermediate layer thicker than 50 {micro}m. The main failure modes were identified based on microstructural analyses.« less
  • Rare earth zirconates are promising materials for use as thermal barrier coatings in gas turbine engines. Among the lanthanide zirconate materials, Sm2Zr2O7 with the pyrochlore structure has lower thermal conductivity and better corrosion resistance against calcium-magnesium-aluminum-silicon oxide (CMAS). In this work, after reaction with CMAS, the pyrochlore structure transforms to the cubic fluorite structure and Ca2Sm8(SiO4)6O2 forms in elongated grain.
  • During creep loading metallic substrates impose deformation on deposited ceramic thermal barrier coatings (TBC). Strain accommodation of the TBC is not attained by plastic deformation, but by means of crack initiation, crack opening, crack propagation or sliding of adjacent crack faces. In technical applications a distinction is made between tolerated or desired cracks perpendicular to the surface, and detrimental cracks parallel to the substrate-coating interface. Thus, TBC can respond to creep deformation by segmentation or spallation, the latter being referred to as failure. The parameters influencing the probability of either segmentation or spallation are temperature, creep rate, magnitude of creepmore » deformation, layer thickness, and microstructure of the TBC. It can be stated that spallation failure probability increases with increasing creep rate, creep deformation, and layer thickness. The presence of pores between single spraying layers also strongly augments the likelihood of spallation. No significant influence of temperature on spallation failure probability can be found in the range from 850 C to 1,050 C. Light microscopy and scanning electron microscopy investigation show that the microstructure of the ceramic TBC changes during creep, and that the density of cracks detected on micrographs with low magnification (x50) increases with increasing creep deformation. On the other hand, the density of microcracks visible with high magnification (x500) is constant, or even decreases with increasing creep deformation. These findings are explained by sintering processes enabled by stress relaxation due to formation of macroscopic cracks perpendicular to the surface as a response to creep deformation. A relationship between microstructural changes and the emission of signals recorded during creep is presented.« less