CMC Coating for Gas Turbine Sealing Surface Finish
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Solution Overview
Problem
Ceramic matrix composites (CMCs) used in gas turbine engines face challenges such as higher production costs, longer manufacturing times, limited geometries, porosity, and inconsistent machining, leading to efficiency losses due to cooling flow leakage and rough surfaces.
Innovation Solution
A coating system comprising specific compositions like S-A-Y and B-A-S materials with defined mass percentages of silicon dioxide, aluminum oxide, and yttrium/barium oxide is applied to CMC components, providing a smooth, thermally stable, and matching coefficient of thermal expansion with the substrate, preventing undulations and gaps in sealing surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMCs are used to replace metallic nickel-based superalloys for high temperature operation, then temperature resistance and mechanical strength are improved, but production cost and manufacturing cycle time increase
Solution Approach 1:
The coating is applied to the CMC component before the component is installed in the gas turbine engine. This preliminary coating step protects the CMC from direct exposure to harsh environments during operation, potentially extending component life and reducing maintenance frequency, thereby improving overall productivity despite the longer initial manufacturing cycle time
Solution Approach 2:
The patent uses a composite coating system consisting of multiple layers with different compositions (e.g., EB-500 environmental barrier coating, TBC thermal barrier coating, BC bond coating). This multi-layer composite structure provides both temperature resistance and protection against environmental degradation, allowing the CMC component to operate at higher temperatures while maintaining durability
2Temperature
If CMCs are used for sealing surfaces, then high temperature resistance is improved, but porosity leads to cooling flow leakage and efficiency losses
Solution Approach 1:
The coating acts as an intermediary layer between the CMC sealing surface and the environment. It fills surface porosity and provides a dense, non-porous barrier that prevents cooling flow leakage while allowing the underlying CMC to maintain its high temperature resistance properties
Solution Approach 2:
The coating is specifically applied to the sealing surfaces of the CMC component where porosity would cause leakage. This localized treatment addresses the sealing efficiency problem at the critical interface without requiring changes to the entire CMC structure, maintaining temperature resistance where needed while eliminating leakage paths
3Shape
If CMCs are machined to create sealing surfaces, then geometry flexibility is improved, but inconsistent material removal creates rough surfaces and undulations
Solution Approach 1:
The coating serves as an intermediary layer that covers the rough machined surface of the CMC component. It provides a smooth, consistent sealing surface that compensates for the underlying roughness caused by inconsistent material removal during machining, while allowing the CMC to maintain its geometric flexibility
Solution Approach 2:
The coating is applied specifically to the sealing surfaces where surface finish consistency is critical. This localized application addresses the manufacturing precision problem at the interface without requiring changes to the machining process or the overall CMC geometry, preserving the geometry flexibility advantage of CMCs
Data Source
AI summary
A coating includes: at least 34.9 percent by mass silicon dioxide; at least 9.1 percent by mass aluminum oxide; and at least 16.1 percent by mass yttrium oxide.