Multilayered Environmental Barrier Coating for SiC Substrates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Environmental barrier coatings for SiC/CMC substrates face challenges such as reduced durability due to oxidation and corrosion in high-temperature, high-pressure environments, with issues like porosity and spalling caused by the formation of liquid phases at interfaces between rare-earth silicate and mullite layers, and excessive silica volatilization.
Innovation Solution
A multilayered environmental barrier coating structure comprising a SiAlON bonding layer, a mullite oxygen shielding layer, a reaction inhibition layer, and a gradient layer that gradually changes from rare-earth disilicate to monosilicate, preventing liquid phase formation and enhancing adhesion between layers, including specific layers like Al2O3, RE3Al5O12, and [(1-x)RE2SiO5-xRE2Si2O7], with ytterbium or lutetium as the rare-earth element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a RE2Si2O7 layer is directly formed on the Si bonding layer, then oxidation resistance is improved, but the layer becomes porous and spalls due to SiO2 transformation to Si(OH)4 and volatilization
Solution Approach 1:
A mullite layer is introduced as an intermediary between the Si bonding layer and the RE2Si2O7 layer. This mullite layer serves as an oxygen shielding layer that prevents excessive oxidation of the Si bonding layer, thereby preventing the formation of thick SiO2-TGO that would transform to Si(OH)4 and cause porosity and spalling of the RE2Si2O7 layer.
2Strength
If excessive silica is present at the interface between rare-earth silicate layer and mullite layer, then bonding is improved, but liquid phase forms at high temperature causing porosity and spalling
Solution Approach 1:
The silica content at the interface between the rare-earth silicate layer and mullite layer is precisely controlled within a specific range (0.1-5 mass%). This parameter control prevents the formation of excessive silica that would create liquid phase at high temperatures, while still maintaining sufficient interfacial bonding strength.
3Temperature
If SiC/CMC substrate is used for high-temperature components, then heat resistance and specific strength are improved, but durability is reduced due to oxidative wear and corrosion by water vapor
Solution Approach 1:
A multilayered environmental barrier coating structure is applied to the SiC/CMC substrate, combining multiple materials (SiAlON bonding layer, mullite oxygen shielding layer, and RE2Si2O7 water vapor shielding layer) with complementary properties. This composite coating system provides comprehensive protection against both oxidative wear and water vapor corrosion, enabling the SiC/CMC substrate to maintain durability in high-temperature water vapor environments.
4Reliability
If mullite layer is added as oxygen shielding layer, then oxidation resistance is improved, but device complexity increases
Solution Approach 1:
The environmental barrier coating is segmented into distinct functional layers: SiAlON bonding layer for substrate attachment, mullite oxygen shielding layer for preventing excessive oxidation, and RE2Si2O7 water vapor shielding layer for preventing water vapor penetration. This segmentation allows each layer to perform its specific function optimally while maintaining overall system reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multilayered coating structure significantly improves adhesion and durability, providing excellent resistance to oxygen and water vapor, thermal shock, and maintaining structural integrity at high temperatures, making it suitable for hot-section components like aeroengine turbines.
Implementation Method 1
the rare-earth silicate has sufficient durability even in high-temperature and high-pressure combustion gas environments such as aeroengines, and further has a thermal expansion coefficient close to that of SiC/CMC
Implementation Method 2
Mullite, denoted as 3Al2O3▪2SiO2, exhibits excellent oxygen shielding property
Implementation Method 3
the rare-earth silicate has sufficient durability even in high-temperature and high-pressure combustion gas environments such as aeroengines
Implementation Method 4
If a RE2Si2O7 layer is directly formed on the surface of a Si bonding layer, part of a SiO2-TGO (Thermally Grown Oxide) layer formed due to oxidation of the Si bonding layer is changed to Si(OH)4 and volatilized
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An environmental resistant coating member 100 includes a SiC long fiber-reinforced ceramics substrate 1 and an environmental barrier coating layer 2 provided on the whole surface of the SiC long fiber-reinforced ceramics substrate 1. The environmental barrier coating layer 2 includes a SiAlON bonding layer 21 laminated on the SiC long fiber-reinforced ceramics substrate 1, a mullite layer 22 laminated on the SiAlON bonding layer 21, a reaction inhibition layer 23 laminated on the mullite layer 22, and a gradient layer 24 formed on the reaction inhibition layer 23 and having a composition that gradually changes from a rare-earth disilicate to a rare-earth monosilicate. The reaction inhibition layer 23 includes at least one of an alumina layer, a garnet layer, and a rare-earth (mono)silicate layer. When the reaction inhibition layer 23 includes two or more of these layers, the two or more layers are formed in the order of the alumina layer, the garnet layer, and the rare-earth (mono)silicate layer from a mullite layer 22 side toward a gradient layer 24 side.