Crystallization Behavior of Air-Plasma-Sprayed Ytterbium-Silicate-Based Environmental Barrier Coatings

2021 ◽  
Author(s):  
Eugenio Garcia ◽  
Hector F. Garces ◽  
Laura R. Turcer ◽  
Hrishikesh A. Bale ◽  
Nitin P. Padture ◽  
...  
Keyword(s):  
Crystallization Behavior ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Environmental Barrier Coatings ◽  
Environmental Barrier ◽  
Plasma Sprayed ◽  
Ytterbium Silicate

Mass Transfer in Yb Silicate Environmental Barrier Coatings at High Temperatures

2018 ◽  
Vol 941 ◽  
pp. 1898-1903
Author(s):  
Satoshi Kitaoka ◽  
Tsuneaki Matsudaira ◽  
Masashi Wada ◽  
Naoki Kawashima ◽  
Daisaku Yokoe ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Oxygen Potential ◽  
Silicate Layer ◽  
Design Guideline ◽  
Barrier Coatings ◽  
Environmental Barrier Coatings ◽  
Environmental Barrier ◽  
Partial Pressures ◽  
Potential Gradients ◽  
Ytterbium Silicate

The oxygen permeabilities of polycrystalline Yb2Si2O7 wafers cut from sintered bodies to serve as models of environmental barrier coatings were determined at temperatures up to 1673 K under various oxygen potential gradients (dµO), produced by exposing the upper and lower surfaces of the wafer to atmospheres with different oxygen partial pressures (PO2). Oxygen permeation proceeded via grain boundary (GB) diffusion of oxygen from the higher PO2 surface to the lower PO2 surface, concurrently with GB diffusion of ytterbium in the opposite direction. Mass transfer analysis allowed for a design guideline for selectively enhancing the structural stability of the ytterbium silicate layer with applying a dµO.

Environmental Barrier Coatings for Silicon Nitride

2011 ◽  
Vol 484 ◽  
pp. 139-144 ◽  
Author(s):  
Hong Fei Chen ◽  
Hagen Klemm
Keyword(s):  
Dip Coating ◽  
Barrier Coatings ◽  
Environmental Barrier Coatings ◽  
Environmental Barrier ◽  
Porous Interface ◽  
Ytterbium Silicate ◽  
Silicate Layers ◽  
Water Vapor Corrosion ◽  
And Diffusion ◽  
Sintering Method

Ytterbium silicate layers were deposited on Si3N4 ceramics as environmental barrier coatings (EBCs) by a dip coating-sintering method. Coated samples were tested in an atmosphere simulating the practical conditions of a gas turbine to investigate water vapor corrosion and recession mechanisms of ytterbium silicate coatings. Prior and after tests, phase compositions and morphologies of the coatings varied as the consequence of the formation of silica at the coating/substrate interface. Due to the evaporation and diffusion of silica into the upper layer, a porous interface was finally found, which led to the spallation of coating.

scholarly journals Correlation of Process Conditions, Porosity Levels and Crystallinity in Atmospherically Plasma Sprayed Yb2Si2O7 Environmental Barrier Coatings

2021 ◽  
Vol 5 (8) ◽  
pp. 198
Author(s):  
Robert Vaßen ◽  
Emine Bakan ◽  
Doris Sebold ◽  
Yoo Jung Sohn
Keyword(s):  
Gas Turbines ◽  
Single Layer ◽  
Hot Water ◽  
Process Conditions ◽  
Standard Material ◽  
Barrier Coatings ◽  
Environmental Barrier Coatings ◽  
Environmental Barrier ◽  
Sic Composites ◽  
Plasma Sprayed

Environmental barrier coatings are necessary to protect fibre reinforced ceramics from high recession rates in fast and hot water vapor-containing gases as they typically are found in the hot gas sections of gas turbines. A standard material to protect SiC/SiC composites is atmospherically plasma sprayed (APS) Yb2Si2O7. For this material, it is difficult to obtain at reasonable substrate temperatures both low porosity and high crystallinity levels during APS. In this paper results of coatings prepared by a so-called high velocity APS process and also more conventional processes are presented. All coatings have been prepared by a single layer deposition method which avoids inter passage porosity bands. Furthermore, the samples were heat-treated in air at 1300 °C for 100 h and the influence of the topcoat density on the growth of the silica scale on the used silicon bond coat was studied.

scholarly journals Steam Degradation of Ytterbium Disilicate Environmental Barrier Coatings: Effect of Composition, Microstructure and Temperature

2022 ◽  
Author(s):  
Daniel Tejero-Martin ◽  
Mingwen Bai ◽  
Acacio R. Romero ◽  
Richard G. Wellman ◽  
Tanvir Hussain
Keyword(s):  
Underlying Mechanism ◽  
Turbine Engines ◽  
Free Standing ◽  
Porosity Level ◽  
Barrier Coatings ◽  
Environmental Barrier Coatings ◽  
Environmental Barrier ◽  
Three Samples ◽  
High Temperature Steam ◽  
Plasma Sprayed

Recession of environmental barrier coatings (EBC) in environments containing steam is a pressing concern that requires further research before their implementation in gas turbine engines can be realized. In this work, free-standing plasma sprayed Yb2Si2O7 coatings were exposed to flowing steam at 1350 °C and 1400 °C for 96 h. Three samples were investigated, one coating with a low porosity level (< 3 %) and 1 wt.% Al2O3 representing traditional EBCs; and two coatings with higher porosity levels (~20 %) representing abradable EBCs. Phase composition and microstructural evolution were studied in order to reveal the underlying mechanism for the interaction between high temperature steam and ytterbium disilicate. The results show depletion of Yb2SiO5 near the surface and formation of ytterbium garnet (Yb3Al5O12) on top of all three coatings due to the reaction with gaseous Al-containing impurities coming from the alumina furnace tubes. The 1 wt.% Al2O3 added to the EBC sample exacerbated the formation of garnet at 1400 °C compared to the abradable samples, which presented lower quantities of garnet. Additionally, inter-splat boundaries were visible after exposure, indicating preferential ingress of gaseous Al-containing impurities through the splat boundaries.

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