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.

Computational investigation of foreign object damage sustained by environmental barrier coatings (EBCs) and SiC/SiC ceramic-matrix composites (CMCs)

2015 ◽  
Vol 11 (2) ◽  
pp. 238-272 ◽  
Author(s):  
Mica Grujicic ◽  
Jennifer Snipes ◽  
Ramin Yavari ◽  
S. Ramaswami ◽  
Rohan Galgalikar
Keyword(s):  
Gas Turbine ◽  
Ceramic Matrix ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Foreign Object ◽  
Barrier Coatings ◽  
Content Type ◽  
Environmental Barrier Coatings ◽  
Foreign Object Damage ◽  
Environmental Barrier

Purpose – The purpose of this paper is to prevent their recession caused through chemical reaction with high-temperature water vapor, SiC-fiber/SiC-matrix ceramic-matrix composite (CMC) components used in gas-turbine engines are commonly protected with so-called environmental barrier coatings (EBCs). EBCs typically consist of three layers: a top thermal and mechanical protection coat; an intermediate layer which provides environmental protection; and a bond coat which assures good EBC/CMC adhesion. The materials used in different layers and their thicknesses are selected in such a way that the coating performance is optimized for the gas-turbine component in question. Design/methodology/approach – Gas-turbine engines, while in service, often tend to ingest various foreign objects of different sizes. Such objects, entrained within the gas flow, can be accelerated to velocities as high as 600 m/s and, on impact, cause substantial damage to the EBC and SiC/SiC CMC substrate, compromising the component integrity and service life. The problem of foreign object damage (FOD) is addressed in the present work computationally using a series of transient non-linear dynamics finite-element analyses. Before such analyses could be conducted, a major effort had to be invested toward developing, parameterizing and validating the constitutive models for all attendant materials. Findings – The computed FOD results are compared with their experimental counterparts in order to validate the numerical methodology employed. Originality/value – To the authors’ knowledge, the present work is the first reported study dealing with the computational analysis of the FOD sustained by CMCs protected with EBCs.

Sign in / Sign up

Export Citation Format

Share Document