Gas Turbine Coating Steps Undercuts Stress Dissipation
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Solution Overview
Problem
Protective coatings in gas turbine engines, such as abradable ceramic coatings for turbine blades and blade outer air seals, are prone to erosion and spalling due to internal stresses, leading to reduced longevity and the need for frequent replacement or refurbishment.
Innovation Solution
The use of a substrate with strategically formed steps and undercuts, combined with a thermally insulating topcoat featuring microstructural discontinuities or faults, reduces internal stresses and prevents bridging during deposition, allowing for a thicker, more durable coating that can withstand high temperatures without delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a protective coating is applied to turbine blades and air seals, then protection from high temperatures is improved, but internal stresses cause erosion and spalling reducing longevity
Solution Approach 1:
The protective coating is segmented into multiple layers (bond coat and topcoat) with distinct functions. The bond coat provides oxidation resistance and thermal barrier, while the topcoat provides erosion and corrosion resistance. This segmentation allows each layer to be optimized for its specific function, reducing overall stress and improving longevity.
Solution Approach 2:
The coating system applies different material compositions and properties to different locations and layers. The bond coat has different characteristics than the topcoat, with each layer tailored to address specific local stresses and environmental conditions it will encounter during operation.
2Strength
If a thicker coating is applied to increase durability, then protection from high temperatures is improved, but internal stresses increase causing delamination and spalling
Solution Approach 1:
Dividing the thick protective coating into multiple thinner layers (bond coat and topcoat) reduces internal stresses within each layer while maintaining overall thickness and protection. The interfaces between layers provide stress relief zones that prevent delamination.
Solution Approach 2:
The coating system uses composite material structure with bond coat and topcoat having different material compositions. This composite approach allows optimization of each layer for specific properties while managing thermal and mechanical stresses through material selection and layer configuration.
3Productivity
If an abradable ceramic coating is used to reduce clearance, then gas flow around blade tips is reduced improving efficiency, but the coating becomes vulnerable to erosion and spalling
Solution Approach 1:
The topcoat is specifically designed with erodible material composition in the regions that contact turbine blades, allowing controlled abrasion to maintain clearance while the bond coat and substrate provide structural support. This local quality optimization allows the coating to be soft enough to abrade cleanly but supported by harder underlying layers.
Solution Approach 2:
The composite coating structure combines erodible topcoat material with more robust bond coat and substrate materials. This allows the topcoat to provide the necessary abradable surface for clearance control while the underlying layers provide structural integrity and resistance to erosion and spalling.
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 solution extends the lifespan of protective coatings by dissipating thermal stresses and preventing cracking, thereby enhancing the durability and efficiency of gas turbine engine components.
Implementation Method 1
a thermally insulating topcoat featuring microstructural discontinuities or faults, reduces internal stresses and prevents bridging during deposition
Implementation Method 2
The solution extends the lifespan of protective coatings by dissipating thermal stresses and preventing cracking
Data Source
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AI summary
A gas turbine engine article (264) includes a substrate (265) that has at least one step (267), and the step (267) includes an undercut (269; 369). A thermally insulating topcoat (284) is disposed on the substrate (265). The thermally insulating topcoat (284) includes at least one fault (298) that extends from the step (267).