Investigation of a single-layer EBC deposited on SiC/SiC CMCs: Processing and corrosion behaviour in high-temperature steam

Nasiri, Nasrin Al; Patra, Nihar Ranjan; Pezoldt, Marc; Colas, Johann; Lee, William

doi:10.1016/j.jeurceramsoc.2018.12.019

Cited by 48 publications

(22 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(c) Regions where an extensive 2nd phase reaction product formed, Figure 5E, seemingly occupying all coating porosity and the entirety of the SiC‐YbDS separation. Second phase reaction products have been reported before during high temperature (>1316°C) steam oxidation of YbDS 17,24,27,31,32 . A lower magnification panoramic cross sectional BSE that is more representative of the single layer specimen interface as a whole is shown in Figure 5F.…”

Section: Resultssupporting

confidence: 54%

Steam oxidation of ytterbium disilicate environmental barrier coatings with and without a silicon bond coat

et al. 2021

View full text Add to dashboard Cite

The current generation of multilayer Si/Yb2Si2O7 environmental barrier coatings (EBCs) are temperature limited by the melting point of Si, 1414°C. To investigate higher temperature EBCs, the cyclic steam oxidation of EBCs comprised of a single layer of ytterbium disilicate (YbDS) was compared to multilayered Si/YbDS EBCs, both deposited on SiC substrates using atmospheric plasma spray. After 500 1‐h cycles at 1300°C in 90 vol%H2O‐10 vol%air with a gas velocity of 1.5 cm/s, both multilayer Si/YbDS and single layer YbDS grew thinner silica scales than bare SiC, with the single layer YbDS forming the thinnest scale. Both coatings remained fully adherent and showed no signs of delamination. Silica scales formed on the single layer coating were significantly more homogeneous and possessed a markedly lower degree of cracking compared to the multilayered EBC. The single layer EBC also was exposed at 1425°C in steam with a gas velocity of 14 cm/s in an alumina reaction tube. The EBC reduced specimen mass loss compared to bare SiC but formed an extensive 2nd phase aluminosilicate reaction product. A similar reaction product was observed to form on some regions of the bare SiC specimen and appeared to partially inhibit silica volatilization. The 1425°C steam exposures were repeated with a SiC reaction tube and no 2nd phase reaction product was observed to form on the single layer EBC or bare SiC.

show abstract

Section: Resultssupporting

confidence: 54%

Steam oxidation of ytterbium disilicate environmental barrier coatings with and without a silicon bond coat

et al. 2021

View full text Add to dashboard Cite

show abstract

“…Preceramic polycarbosilane polymers are commonly used as precursors to make ceramic fibers 10,39 and ceramic matrix. [7][8][9]40,41 The chemical and volume changes that accompany ceramization of the polymer during pyrolysis have been documented in several studies. For example, see Refs [39][40][41][42].…”

Section: Methodsmentioning

confidence: 99%

Evaluating steam oxidation kinetics of environmental barrier coatings

et al. 2021

View full text Add to dashboard Cite

Environmental barrier coatings (EBCs) are a commercially proven means of protecting SiC-based materials in gas turbine environments. However, there are little specific data in the literature on the impact of coatings like Yb 2 Si 2 O 7 on preventing accelerated SiO 2 growth in the presence of H 2 O. Quantification of reduced rates are necessary for evaluating and comparing EBC effectiveness and incorporation of silica growth rates into future EBC lifetime models. In this study, baseline kinetics of silica formation on bare Si and chemically vapor deposited (CVD) SiC in the 1250-1425℃ range were obtained via 100 h isothermal exposures in dry air and steam environments utilizing a SiC reaction tube to mitigate specimen volatility. An Arrhenius plot of the resulting rates was constructed, representing baseline minimum and maximum rates for Si and SiC oxidation at ambient pressure. Various EBC systems on CVD SiC substrates including air plasma sprayed (APS) EBCs with and without a Si bond coating and with surface roughening to enhance Yb 2 Si 2 O 7 adhesion were subjected to 1-h furnace cycle testing in air with 90vol%H 2 O at 1250-1350℃ for up to 500 cycles. After exposure, silica formation rates were measured and compared to the baseline rates to assess EBC effectiveness, where EBC effectiveness is gauged as the propensity to reduce underlying rates of silica formation. With a Si bond coating, a ~180 µm Yb 2 Si 2 O 7 (YbDS) top coating reduced rates over the entire 1250°-1350℃ range. Without a Si bond coating, ~60 µm (YbDS) coatings deposited directly onto CVD SiC exhibited poor adhesion, and had to be deposited onto substrates with enhanced roughness at 1350℃. While exhibiting good adhesion at 1350℃, overall the single layer YbDS coating exhibited a decreasing effectiveness from 1250° to 1350℃.

show abstract

“…In dry oxygen, they demonstrate high oxidation resistance due to the formation of a silica protective layer [2]. However, in water vapor containing combustion environments, this protective layer is prone to volatilization, which limits the application of uncoated SiC/SiC-CMCs [7] [8]. Thus, additional oxidation and corrosion protection is needed, which is often in the form of a multi-layered coating system called Environmental Barrier Coating (EBC).…”

Section: Introductionmentioning

confidence: 99%

Oxygen Permeability and Its Role in Governing Life of YbDS Environmental Barrier Coatings

Singh

Nganbe

Chen

2021

Thermal Spray 2021: Proceedings From the International Thermal Spray Conference

View full text Add to dashboard Cite

The growth kinetics of thermally grown oxide (TGO) silica in Yb-disilicate (YbDS) environmental barrier coatings (EBCs) significantly affects the durability of EBCs. The oxygen permeability can control the TGO growth kinetics and thus could play an essential role in determining EBCs life. Therefore; the oxygen permeability constant of YbDS and TGO is systematically evaluated and quantified in terms of thermodynamics using defect reactions and the parabolic rate constant (kp); respectively. Dry oxygen and wet oxygen conditions as well as different temperatures; partial pressures and top coat modifiers are investigated. The results offer evidence that the oxygen permeability constant for the YbDS top coat is an order of magnitude higher than for the TGO. As such; the TGO hinders the oxidant diffusion stronger; proving to be the diffusion rate controlling layer. Moreover; water vapor strongly increases the oxygen permeability with defect reactions playing a key role. It is suggested that the mass transfer through the top coat is primarily by outward ytterbium ion diffusion and inward oxygen ion movement; with the latter being dominant; particularly in wet environments. The effect of top coat modifiers on oxidant permeation is composition sensitive and seems to be related to their interaction with oxygen ions and their mobility.

show abstract

Investigation of a single-layer EBC deposited on SiC/SiC CMCs: Processing and corrosion behaviour in high-temperature steam

Cited by 48 publications

References 30 publications

Steam oxidation of ytterbium disilicate environmental barrier coatings with and without a silicon bond coat

Steam oxidation of ytterbium disilicate environmental barrier coatings with and without a silicon bond coat

Evaluating steam oxidation kinetics of environmental barrier coatings

Oxygen Permeability and Its Role in Governing Life of YbDS Environmental Barrier Coatings

Contact Info

Product

Resources

About