CMAS Mitigation 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 chemically with the coatings at high temperatures, leading to material loss and reduced component life.
Innovation Solution
The development of EBCs with CMAS mitigation capability, comprising specific outer and transition layers such as AeAl2O19, AeHfO3, ZnAl2O4, MgAl2O4, Ln4Al2O9, and HfO2, which provide a barrier against CMAS deposition and volatilization, thereby protecting the ceramic components from high-temperature steam and mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional EBCs (bond coat, transition layer, outer layer) are used to protect ceramic components, then environmental protection and hermetic seal are provided, but the coatings are susceptible to CMAS deposition and chemical interaction at high temperatures leading to material loss
Solution Approach 1:
The patent introduces a CMAS barrier layer as an intermediary between the outer layer and the CMAS deposits. This barrier layer specifically prevents CMAS from reaching and reacting with the underlying EBC layers, while allowing the EBC to maintain its environmental protection function. The barrier layer acts as a dedicated mediator that addresses the CMAS issue without disrupting the existing EBC architecture.
Solution Approach 2:
The patent employs composite material structures in multiple forms: the EBC itself is a composite of multiple layers (bond coat, transition layer, outer layer), and the CMAS barrier layer is applied as an additional composite component. The use of composite materials allows each layer to perform its specific function - the EBC provides environmental protection while the barrier layer provides CMAS resistance, together creating a multi-functional coating system.
2Reliability
If the outer layer is made hermetic to prevent hot gas penetration, then protection against corrosive gases is improved, but mechanical stress from thermal expansion mismatch increases
Solution Approach 1:
The patent divides the coating system into functionally distinct segments: the EBC (with its bond coat, transition layer, and outer layer) that provides environmental protection and hermetic seal, and the separate CMAS barrier layer that addresses CMAS deposition. This segmentation allows each layer to be optimized for its specific function without compromising the other, enabling the outer layer to remain hermetic while the overall system manages thermal stress through the layered architecture.
Solution Approach 2:
The patent modifies the coating system by adding the CMAS barrier layer, which changes the physical and chemical parameters of the coating structure. This addition allows the system to maintain the hermetic properties of the outer layer while introducing a new parameter (the barrier layer's presence) that mitigates the harmful effects of CMAS, thereby indirectly addressing the stress issue by preventing material degradation.
3Productivity
If operating temperatures are increased to improve engine efficiency, then energy conversion is improved, but high temperature durability of components deteriorates
Solution Approach 1:
The patent applies the CMAS barrier layer and optimized EBC structure as a preliminary protective measure before the component is exposed to high-temperature operation. This preliminary action of coating the ceramic component with CMAS-resistant and environmentally protective layers ensures that when the component operates at high temperatures for improved efficiency, the coating system is already in place to prevent CMAS deposition and chemical interaction, thereby maintaining durability at elevated temperatures.
Solution Approach 2:
The patent converts the harmful effect of CMAS deposition into a beneficial outcome by introducing the CMAS barrier layer. Instead of allowing CMAS to directly damage the EBC and reduce durability, the barrier layer captures and isolates the CMAS, preventing it from causing harm. This allows the component to operate at higher temperatures for improved efficiency while the barrier layer sacrificially protects the underlying structure, effectively converting the potential harm of CMAS into a controlled interaction that preserves component integrity.
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 prevent CMAS-induced degradation and material loss, maintaining the integrity and longevity of ceramic components in high-temperature environments by forming a robust barrier against CMAS and steam penetration, ensuring the hermetic seal and mechanical integrity of the coatings.
Implementation Method 1
At a porosity of about 10% or less, a hermetic seal to the hot gases in the combustion environment can form
Implementation Method 2
BSAS and CMAS chemically interact at high temperatures, i.e. above the melting point of CMAS (approximately 1150° C. to 1650° C.)
Implementation Method 3
the reaction byproducts formed by the interaction of BSAS and CMAS are detrimental to EBCs as well as being susceptible to volatilization in the presence of steam at high temperatures
Implementation Method 4
the bond coat layer serves as an oxidation barrier to prevent oxidation of the substrate
Implementation Method 5
it can be beneficial to have some layers of higher porosity range to mitigate mechanical stress induced by any thermal expansion mismatch between the coating materials and the substrate
Data Source
AI summary
Environmental barrier coating having CMAS mitigation capability for oxide components. In one embodiment, the barrier coating includes an outer layer selected from AeAl2O19, AeHfO3, AeZrO3, ZnAl2O4, MgAl2O4, Ln4Al2O9, Lna4Ga2O9, Ln3Al5O12, Ln3Ga5O12, and Ga2O3.