BOAS Coating Structure for CMAS Resistance and Abradability
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Solution Overview
Problem
Existing blade outer air seals (BOAS) in gas turbine engines face challenges with temperature and environmental resistance, particularly due to the attack by calcia-magnesia-alumino-silicate (CMAS) which can lead to coating failure and reduced lifespan.
Innovation Solution
A multilayer coating system is applied to the BOAS, comprising a bond coat, an environmental barrier coating (EBC) with refractory metal oxides like HfSiO4 or ZrSiO4, and a CMAS-resistant abradable layer with porosity between 15-40%, designed to accommodate CMAS infiltration while maintaining abradability and protecting the underlying structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is applied to the BOAS to resist CMAS attack, then the environmental resistance is improved, but the abradability may deteriorate
Solution Approach 1:
The coating is divided into multiple functional layers: an environmental barrier coating layer (EBCL) for CMAS resistance and an abradable layer for controlled abrasion. This segmentation allows each layer to specialize in one function, resolving the contradiction between environmental resistance and abradability.
Solution Approach 2:
The coating uses composite material structures where the EBCL contains refractory metal oxides (HfSiO4, ZrSiO4) for chemical stability against CMAS, while the abradable layer uses porous ceramic materials (silicon carbide, silicon oxycarbide) that provide both CMAS absorption and controlled abrasion characteristics.
2Reliability
If the abradable layer has high porosity to accommodate CMAS infiltration, then the CMAS resistance is improved, but the structural strength may worsen
Solution Approach 1:
The abradable layer is designed with controlled porosity (15-40%) to absorb and accommodate CMAS infiltration through capillary action, preventing reactive crystallization. The porous structure provides CMAS resistance while the underlying dense EBCL and bond coat maintain structural strength.
Solution Approach 2:
The porous abradable layer acts as a cushioning layer that anticipates and absorbs CMAS infiltration before it can reach and damage the underlying structural components. This pre-positioned absorption capacity protects the structure from CMAS-induced damage.
3Reliability
If a multilayer coating system is applied to improve temperature and environmental resistance, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The coating system is segmented into three distinct layers with specific functions: bond coat for adhesion, environmental barrier coating layer for CMAS and oxidation resistance, and abradable layer for blade tip clearance control and CMAS absorption. This segmentation allows each layer to be optimized independently while working together as a system.
Solution Approach 2:
The abradable layer serves multiple functions simultaneously: it provides controlled abrasion for blade tip clearance management, absorbs CMAS through its porous structure, and acts as a thermal barrier. This multi-functionality reduces the need for additional separate components.
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 coating system effectively resists CMAS attack, maintaining the BOAS's integrity and extending its lifespan by absorbing CMAS without reactive crystallization, thus enhancing the engine's operational reliability.
Implementation Method 1
Pores of the abradable layer are configured to receive molten calcia-magnesia-alumino-silicate (CMAS)
Implementation Method 2
The environmental barrier coating is nonreactive with respect to calcia-magnesia-alumino-silicate (CMAS). The environmental barrier coating layer includes at least one refractory metal oxide such as HfSiO4 or ZrSiO4
Data Source
AI summary
A blade outer air seal includes a center web having a radially inner face and a radially outer face, at least one mounting arm extending from the radially outer face, and a coating disposed on the radially inner face. The coating includes an environmental barrier coating layer and an abradable layer disposed on the environmental barrier layer. The abradable layer has a porosity of between about 15 percent and about 40 percent. A gas turbine engine and a method of protecting a blade outer air seal are also disclosed.