CMC Honeycomb Base for Abradable Coating Spalling
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Solution Overview
Problem
Existing blade outer air seals in gas turbine engines face challenges with coating spalling and erosion, leading to reduced effectiveness and potentially requiring frequent replacement.
Innovation Solution
A blade outer air seal with a ceramic matrix composite (CMC) material and a geometrically segmented abradable coating (GSAC) is used, featuring a honeycomb layer that reduces spalling by providing segmentation cracks and additional structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional coating is applied on blade outer air seal, then the seal provides thermal and environmental protection, but the coating suffers from spalling and erosion leading to reduced effectiveness
Solution Approach 1:
The coating is designed with a geometrically segmented structure featuring a honeycomb layer with cells that create segmentation cracks. This segmentation allows the coating to break in a controlled manner, preventing catastrophic spalling and maintaining structural integrity under thermal and mechanical stress.
Solution Approach 2:
The coating employs a composite structure combining a CMC honeycomb base layer with an abradable coating layer. This composite design provides both structural support from the honeycomb and protective functionality from the abradable coating, enhancing resistance to spalling and erosion while maintaining thermal protection.
2Reliability
If the blade outer air seal operates in harsh thermal and mechanical environments, then it provides necessary sealing function, but the coating experiences erosion and spalling over time
Solution Approach 1:
The honeycomb layer is positioned beneath the abradable coating to provide structural support and cushioning before the coating is subjected to severe thermal and mechanical stresses. This pre-positioned support structure prevents premature coating failure and extends service life in harsh environments.
Solution Approach 2:
The coating structure incorporates controlled segmentation cracks that change the mechanical parameters of the coating, allowing it to accommodate thermal expansion and stress variations. This parameter modification prevents uncontrolled spalling and maintains sealing function durability under varying operational conditions.
3Temperature
If a dense solid coating is used for thermal protection, then it provides good thermal barrier properties, but it is prone to spalling under thermal stress
Solution Approach 1:
The honeycomb layer introduces a controlled porous structure beneath the thermal barrier coating. This porosity provides thermal insulation while creating segmentation cracks that prevent catastrophic spalling. The porous honeycomb structure maintains thermal barrier performance while significantly improving resistance to thermal stress-induced spalling.
Data Source
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AI summary
A method of forming a blade outer air seal includes applying a cavity layer (130) that has a plurality of cavities (134) to a radially inner side of a seal body. The cavity layer (130) is coated with an abradable coating (132).