Gas Turbine Seal Columnar Microstructure Thermal Stress
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Solution Overview
Problem
Conventional blade outer air seals in gas turbine engines are vulnerable to cracking and corrosion due to thermal gradients caused by cooling methods, leading to accelerated seal degradation and coating failure under high temperature conditions.
Innovation Solution
A gaspath layer with a columnar microstructure is bonded to the substrate of the seal member, allowing for thermal expansion primarily in the radial direction, reducing stress and microcracking, and enabling the use of materials suited for structural and thermal mechanical fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If internal cooling passages or back-side impingement cooling are used to resist high temperatures, then temperature resistance is improved, but thermal gradient through the seals increases causing accelerated seal corrosion and coating cracking
Solution Approach 1:
The seal member is designed with a gaspath layer having a columnar microstructure that is directionally solidified to provide different properties in different directions. The columnar grains are oriented with long axes perpendicular to the radially inner side, creating anisotropic thermal expansion characteristics that allow radial expansion while maintaining structural integrity, thus locally optimizing the material properties to withstand thermal gradients without cracking
Solution Approach 2:
The seal member comprises a composite structure with a substrate and a gaspath layer bonded to it. The gaspath layer has a specific columnar microstructure with different composition and properties than the substrate, creating a composite material system that combines the benefits of both layers - the substrate provides structural support while the gaspath layer provides thermal resistance and fatigue resistance
2Object-affected harmful factors
If conventional coatings are applied to protect from erosion and oxidation, then protection capability is improved, but vulnerability to cracking and coating spall increases under thermal stress
Solution Approach 1:
The gaspath layer is designed with specific compositional parameters including chromium content of 15-30 wt%, nickel content of 10-25 wt%, and other alloying elements to optimize both protective properties and thermal mechanical properties. The columnar microstructure with specific grain orientation and size parameters provides a parameter optimization that balances protection capability with resistance to thermal stress and cracking
Data Source
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AI summary
A gas turbine engine article (30) includes a substrate (50) extending between two circumferential sides, a leading edge (42), a trailing edge (44), an inner side (48) for resisting hot engine exhaust gases, and an outer side (46). A gaspath layer (52) is bonded to the inner side (48) of the substrate (50) and includes a metallic alloy having a columnar microstructure.