Compressor Inner Air Seal Coating for Crack-Resistant Sealing
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Solution Overview
Problem
Gas turbine engines face aerodynamic efficiency losses due to air leakage between compressor blades and the casing, and existing abrasive coatings on rotor lands experience thermal and mechanical stress, leading to crack formation and spallation.
Innovation Solution
A compressor inner air seal system comprising a bond coat on a rotor land, an interlayer of alumina, and an abrasive layer of oxide ceramic with a Mohs hardness of 7 or higher, applied at specific temperature ranges and thicknesses, with an optional transition layer to enhance durability and prevent spallation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer abrasive coating is applied on the rotor land, then the sealing function is provided, but the coating experiences thermal and mechanical stress leading to crack formation and spallation
Solution Approach 1:
The coating system is divided into three distinct layers: a bond coat layer (3-6 mils) as the base, an interlayer (0.1-5.0 mils) with intermediate properties, and an abrasive layer (2-20 mils) providing sealing function. This segmentation allows each layer to be optimized for its specific function and reduces stress concentration that would occur in a single-layer system.
Solution Approach 2:
The patent uses composite material structure with different ceramic compositions in each layer. The bond coat may use NiCrAlY or similar alloys, the interlayer uses alumina or other ceramics with intermediate thermal and mechanical properties, and the abrasive layer uses high-hardness materials like alumina or silicon carbide. This composite structure provides gradual transition of properties, reducing thermal and mechanical stress.
2Strength
If the abrasive layer is applied at high temperature to ensure proper bonding, then the coating adhesion is improved, but thermal stress increases causing cracks and spallation
Solution Approach 1:
The patent specifies applying the abrasive layer at a temperature 400-1400°F less than the interlayer application temperature. The interlayer is applied at 600-1600°F, while the abrasive layer is applied at a reduced temperature that still ensures proper bonding but minimizes thermal stress and prevents crack formation.
3Loss of energy
If the gap at compressor blade tips is reduced to minimize air leakage, then aerodynamic efficiency is improved, but the blade tips may rub against and engage the seal material causing wear
Solution Approach 1:
The coating system provides localized abradability at the seal interface where blade tip contact occurs. The abrasive layer with Mohs hardness of 7 or higher is specifically designed to be engaged by blade tips, allowing controlled wear of the seal material while protecting the blade tips from damage.
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 effectively minimizes air leakage and enhances the durability of the abrasive coating by reducing thermal and mechanical stress, preventing crack propagation and improving the mating surface between the blades and the seal, thus optimizing the aerodynamic efficiency of gas turbine engines.
Implementation Method 1
The interlayer is applied at a temperature of 600 to 1600°F (315 to 872°C). The abrasive layer is applied at a temperature 400 to 1400°F (222°C to 778°C) less than the temperature used to apply the interlayer.
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
An inner air seal includes a bond coat disposed on a substrate, an interlayer disposed on the bond coat, and an abrasive layer disposed on the interlayer.