CMAS Mitigation Environmental Barrier Coatings for Ceramic Substrates
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Solution Overview
Problem
Current environmental barrier coatings (EBCs) used in ceramic substrate components of gas turbine engines are susceptible to degradation due to the formation of calcium magnesium aluminosilicate (CMAS) deposits, which interact with the coatings at high temperatures, leading to material loss and reduced component life.
Innovation Solution
The development of EBCs with a bond coat layer comprising aluminide-alumina TGO, combined with specific transition and outer layers such as AeAl2O19, AeHfO3, ZnAl2O4, and Ln4Al2O9, to provide CMAS mitigation capability, preventing degradation and material loss in high-temperature environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional EBCs (bond coat + transition layer + outer layer) are used for ceramic substrate components, then the components can operate in high-temperature environments, but the coatings are susceptible to CMAS deposition and degradation at temperatures above 1150°C
Solution Approach 1:
The coating system is divided into multiple functional layers: a porous transition layer for stress relief, a hermetic barrier layer for CMAS and steam protection, and an outer layer for environmental resistance. Each layer performs a specific function to collectively resolve the contradiction between high-temperature operation and coating durability.
Solution Approach 2:
The patent employs composite coating structures combining different materials with complementary properties: porous mullite or BSAS for stress management, dense barium aluminosilicate for hermetic barrier properties, and various outer layer materials for oxidation and corrosion resistance. This composite approach enables the coating to withstand CMAS deposition and high-temperature steam environments.
2Object-affected harmful factors
If the transition and outer layers are made hermetic to protect against hot gases, then protection is improved, but mechanical stress from thermal expansion mismatch increases
Solution Approach 1:
The coating is segmented into layers with different porosity levels: a porous transition layer that accommodates thermal expansion stress through its compliant structure, and a hermetic barrier layer that provides protection against hot gases and CMAS. This segmentation allows each layer to optimize its function without compromising the other.
Solution Approach 2:
Different regions of the coating have different properties: the transition layer near the substrate is porous and compliant for stress relief, while the barrier layer is dense and hermetic for protection. This local differentiation of properties resolves the contradiction between mechanical compliance and environmental protection.
3Weight of moving object
If silicon-based CMCs and monolithic ceramics are used to decrease weight and increase temperature capability, then efficiency is improved, but the materials undergo oxidation and steam volatilization leading to material loss
Solution Approach 1:
The environmental barrier coating acts as an intermediary layer between the silicon-based ceramic substrate and the harsh combustion environment. It provides a protective interface that prevents direct exposure to oxidizing and steam-containing gases, thereby preventing oxidation and volatilization of the substrate materials while allowing the lightweight ceramic components to operate at high temperatures.
Solution Approach 2:
The coating creates an inert protective environment around the ceramic substrate by forming a hermetic barrier that excludes reactive gases. The dense barrier layer prevents contact between the substrate and corrosive combustion products, effectively creating a chemically inert environment that prevents material loss.
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
These EBCs effectively mitigate CMAS interactions, maintaining the integrity and longevity of ceramic components by preventing material loss and maintaining a hermetic seal against corrosive gases, thus enhancing the performance and lifespan of components in gas turbine engines.
Implementation Method 1
the bond coat layer serves as an oxidation barrier to prevent oxidation of the substrate
Implementation Method 2
At a porosity of about 10% or less, a hermetic seal to the hot gases in the combustion environment can form
Implementation Method 3
mechanical stress induced by any thermal expansion mismatch between the coating materials and the substrate
Implementation Method 4
the silicon oxide reacts rapidly with high temperature steam, such as found in gas turbine engines, to form volatile silicon species
Data Source
Figure 1
AI summary
Environmental barrier coatings having CMAS mitigation capability for silicon- containing components. In one embodiment, the barrier coating includes a bond coat layer comprising aluminide-alumina TGO; and an outer layer selected from the group consisting of AeA112O19, AeHfO3, AeZrO3, ZnA12O4, MgA12O4, Ln4A12O9, Lna4Ga2O9, Ln3A15O12, Ln3Ga5O12, Ga2O3, HfO2, and LnPO4. "Ae" represents Mg, Ca, Sr, Ba and mixtures thereof. "Ln" represents Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof. "Lna" represents La, Ce, Pr, Nd, Pm, Sm, Eu, Gd and mixtures thereof.