CMAS Mitigation Layer for Environmental Barrier Coatings
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Solution Overview
Problem
Current environmental barrier coatings (EBCs) for gas turbine engine components are vulnerable to CMAS deposits, which interact chemically at high temperatures, leading to material loss and reduced component life due to volatilization in steam environments.
Innovation Solution
Incorporating a CMAS mitigation layer comprising rare earth elements, rare earth oxides, zirconia, hafnia, magnesium oxide, cordierite, and aluminum phosphate into the EBC, either as a separate layer or integrated with BSAS, to prevent degradation from CMAS reactions and volatilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BSAS is used in the transition or outer layer to provide environmental protection, then the coating provides hermetic seal and mechanical integrity, but CMAS interacts with BSAS at high temperatures causing material loss and coating degradation
Solution Approach 1:
A CMAS mitigation layer comprising rare earth elements, rare earth oxides, zirconia, hafnia, magnesium oxide, cordierite, and aluminum phosphate is introduced as an intermediary between the CMAS deposits and the BSAS-containing EBC layers. This mitigation layer acts as a barrier that prevents direct chemical interaction between CMAS and BSAS, thereby eliminating the harmful reaction while preserving the protective function of the original coating system.
2Reliability
If the EBC layers are made hermetic to prevent hot gas penetration, then corrosion protection is improved, but thermal expansion stress from thermal mismatch between coating and substrate increases
Solution Approach 1:
The EBC system is designed with different layers having different porosity characteristics tailored to their specific functions. The CMAS mitigation layer and certain transition layers are designed with controlled porosity to accommodate thermal expansion stresses, while other layers maintain hermetic seals for corrosion protection. This localized differentiation of properties allows simultaneous achievement of both protection and stress management.
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 CMAS mitigation compositions effectively prevent material loss and maintain the integrity of EBCs, reducing the impact of CMAS interactions and extending the lifespan of ceramic components in high-temperature environments.
Implementation Method 1
BSAS and CMAS chemically interact at high temperatures, i.e. above the melting point of CMAS (approximately 1150° C. to 1650° C.)
Implementation Method 2
In dry, high temperature environments, silicon-based (nonoxide) CMCs and monolithic ceramics undergo oxidation to form a protective silicon oxide scale
Implementation Method 3
the silicon oxide reacts rapidly with high temperature steam, such as found in gas turbine engines, to form volatile silicon species
Implementation Method 4
The transition layer may typically comprise mullite, barium strontium aluminosilicate (BSAS), and various combinations thereof
Data Source
AI summary
Methods of making components having calcium magnesium aluminosilicate (CMAS) mitigation capability involving providing a component; applying an environmental barrier coating to the component, the environmental barrier coating having a separate CMAS mitigation layer including a CMAS mitigation composition selected from rare earth elements, rare earth oxides, zirconia, hafnia partially or fully stabilized with alkaline earth or rare earth elements, zirconia partially or fully stabilized with alkaline earth or rare earth elements, magnesium oxide, cordierite, aluminum phosphate, magnesium silicate, and combinations thereof.