Blade Outer Air Seal Multilayer Coating for Rub Durability
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Solution Overview
Problem
There is a need for blade outer air seals (BOAS) in gas turbine engines with improved temperature and environmental resistance, as well as enhanced rub performance to withstand the harsh operating conditions.
Innovation Solution
A multilayer coating system is applied to the BOAS, comprising a bond coat, an environmental barrier coating layer, and an abradable layer with specific Mohs hardness and porosity ranges, along with materials like hafnon or YbDS, to provide durability and protect against CMAS infiltration and erosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer coating is used on the blade outer air seal, then the structure is simple and manufacturing is easier, but the temperature and environmental resistance is insufficient
Solution Approach 1:
The coating system is divided into three distinct functional layers: a bond coat layer for adhesion and oxidation resistance, an environmental barrier coating layer for chemical protection against CMAS and sulfur, and an abradable layer for mechanical durability and rub accommodation. This segmentation allows each layer to optimize its specific function, resolving the contradiction between manufacturing simplicity and environmental resistance.
Solution Approach 2:
The patent employs a composite coating structure combining different material systems with complementary properties. The bond coat uses aluminum-rich materials for oxidation resistance, the EBC layer uses rare earth silicates or aluminosilicates for chemical barrier properties, and the abradable layer uses porous materials with controlled hardness. This composite approach achieves superior overall performance that no single material could provide alone.
2Strength
If the abradable layer has high hardness to resist wear, then wear resistance improves, but rub performance and durability during tip interaction deteriorate
Solution Approach 1:
The abradable layer is engineered with specific parameter ranges: Mohs hardness between 3.5 and 7.5 and porosity between 15% and 40%. These controlled parameters create an optimal balance where the material is soft enough to accommodate blade tip rub interactions and maintain sealing, yet durable enough to resist excessive wear and protect the underlying structure.
Solution Approach 2:
The abradable layer incorporates controlled porosity (15-40%) which provides compliance and damping characteristics essential for accommodating dynamic blade tip interactions. The porous structure allows the material to deform elastically during rub events while maintaining structural integrity, resolving the contradiction between hardness for wear resistance and softness for rub performance.
3Ease of operation
If the abradable layer has high porosity to improve abradability, then rub accommodation improves, but environmental resistance and structural integrity worsen
Solution Approach 1:
The coating system separates the environmental barrier function (EBC layer with low porosity) from the abradable function (top layer with high porosity). The EBC layer acts as a dense protective barrier against CMAS and sulfur infiltration, while the porous abradable layer provides compliance and wear resistance. This segmentation resolves the contradiction by assigning different porosity requirements to different functional layers.
Solution Approach 2:
The environmental barrier coating layer serves as an intermediary between the substrate and the porous abradable layer. It provides the environmental protection that would be compromised by high porosity, while allowing the abradable layer to maintain its porous structure for optimal rub accommodation. The EBC layer mediates between the conflicting requirements of environmental resistance and abradability.
4Reliability
If the coating system includes multiple layers with specific material compositions, then temperature and environmental resistance improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent specifies controlled parameter ranges for each layer (thickness, composition, porosity, hardness) rather than requiring exact values, providing manufacturing flexibility. The abradable layer hardness is specified as Mohs 3.5-7.5 and porosity 15-40%, allowing various material compositions to meet the performance requirements. This parametric approach reduces manufacturing complexity while maintaining reliability.
Solution Approach 2:
Each coating layer is optimized with specific local properties: the bond coat for adhesion and oxidation resistance, the EBC layer for chemical barrier properties, and the abradable layer for mechanical compliance. This local optimization allows each layer to use materials and structures best suited to its specific function, achieving high overall reliability without requiring every layer to be equally complex.
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 significantly improves the durability and longevity of the BOAS by accommodating tip rub interactions while resisting environmental attacks, extending the life of the turbine blades and maintaining efficiency.
Implementation Method 1
The abradable layer has a porosity of 15% to 40%
Implementation Method 2
The abradable layer has a Mohs hardness of 3.5 to up to less than 7.5
Implementation Method 3
an environmental barrier coating layer... to protect against CMAS infiltration and erosion
Implementation Method 4
the difference in the coefficient of thermal expansion CTE of the abradable layer and the radially inner face of the blade outer air seal is less than 50 percent
Implementation Method 5
the melting point of the abradable layer is above 1,550 °C
Data Source
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AI summary
A blade outer air seal (105) includes a center web (105a) having a radially inner face (106) and a radially outer face, at least one mounting arm (105b) extending from the radially outer face, and a coating (200) disposed on the radially inner face (106). The coating (200) includes an environmental barrier coating layer and an abradable layer disposed on the environmental barrier layer. The abradable layer has a Mohs hardness of 3.5 to 7.5 and the porosity of the abradable layer is chosen in view of the Mohs hardness, which significantly improves the durability of the abradable layer. A gas turbine engine and a method of protecting a blade outer air seal (105) are also disclosed.