Recession Resistant Ceramic Matrix Composites Coatings
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Solution Overview
Problem
Ceramic matrix composites (CMCs) face significant challenges due to the loss of thickness caused by the reaction with moisture in combustion gases, leading to recession, and existing environmental barrier coatings (EBCs) are prone to spallation, which exacerbates the issue, limiting their use in high-temperature applications beyond 1399°C (2550 F) due to silicon-based coatings melting and volatilization of silicon as silicon hydroxide.
Innovation Solution
A chemically stable porous oxide layer is introduced, which acts as a diffusion barrier, reducing the recession rate by over an order of magnitude, and a two-phase silicon and oxide layer is used to delay substrate recession, providing improved structural integrity and resistance against spallation, allowing operation at higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon-based environmental barrier coatings are used to protect CMCs from recession, then the CMCs are protected from moisture reaction, but the coatings melt and volatilize at temperatures above 1399°C (2550 F)
Solution Approach 1:
The patent changes the material composition parameter by replacing silicon-based coatings with aluminum-based coatings. This parameter change allows the coating to maintain structural integrity at temperatures above 1399°C (2550 F) where silicon would melt and volatilize, while still providing protection against moisture reaction and recession of the CMC substrate.
Solution Approach 2:
The patent employs composite material structures combining aluminum-based coatings with ceramic matrix composites. This composite approach creates a protective layer that resists both thermal degradation (above 1399°C) and chemical attack from moisture, solving the contradiction between high-temperature stability and recession protection.
2Reliability
If multi-layer environmental barrier coatings are used to protect CMCs, then recession resistance is improved, but the coatings are prone to spallation which exposes the substrate to moisture
Solution Approach 1:
The patent applies aluminum-based coatings that can be applied directly to the CMC surface and provide immediate protection. The coating is designed to form a stable, adherent layer that resists spallation, providing a durable protective barrier that eliminates the need for complex multi-layer structures and reduces the risk of spallation-induced substrate exposure.
3Productivity
If the ceramic matrix composite operates at higher temperatures to improve efficiency, then engine efficiency increases, but the durability and resistance to recession decrease
Solution Approach 1:
The aluminum-based coating acts as an intermediary protective layer between the CMC substrate and the harsh high-temperature combustion environment. This intermediate coating layer absorbs the thermal and chemical stress, allowing the CMC to operate at higher temperatures for improved engine efficiency while maintaining structural integrity and resistance to recession through the coating's protective action.
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 porous oxide layer significantly reduces the recession rate of CMCs, extending their lifespan and maintaining structural integrity even when EBCs spall, enabling operation at temperatures up to 1482°C (2700 F) with reduced volatilization and improved mechanical integrity.
Implementation Method 1
A chemically stable porous oxide layer is introduced, which acts as a diffusion barrier, reducing the recession rate by over an order of magnitude
Implementation Method 2
EBCs developed to date are multi-layer coatings with a bond coat of silicon or silicon-containing material, which on oxidation forms silicon oxide
Implementation Method 3
Volatilization of silicon as silicon hydroxide is one of the key problems with such composites because it leads to loss of thickness with time
Implementation Method 4
silicon melts at temperatures around 1399 °C (2550 F). Therefore, silicon-based coatings are currently not practical at temperatures over about 1399 °C (2550 F)
Data Source
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AI summary
The disclosure relates generally to recession resistant gas turbine engine articles that comprise a silicon containing substrate, and related coatings and methods. The present disclosure is directed, inter alia, to an engine article comprising a silicon substrate which is coated with a chemically stable porous oxide layer. The present disclosure also relates to articles comprising a substrate and a bond coat on top comprising a two phase layer of interconnected silicon and interconnected oxide, followed by a layer of silicon. The present disclosure further relates to a recession resistant article comprising an oxide in a silicon containing substrate, such that components of the silicon containing substrate is interconnected with oxides dispersed in the substrate and form the bulk of the recession resistant silicon containing article.