Abradable Coating Safety Fuse for Gas Turbine Thermal Runaway
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Solution Overview
Problem
Cantilevered vane rotor coatings in gas turbine engines face issues with thermal conductivity leading to runaway events and coating spallation during high rub interactions, causing potential damage and inefficiency due to inadequate clearance and thermal expansion.
Innovation Solution
A multi-layer coating system comprising a metallic bond coat, a ceramic layer for thermal insulation and as a fuse, and an abradable layer, where the ceramic layer is twice as thick as the abradable layer, designed to spall off during high rub interactions and maintain optimal clearance between rotor and vane tips, preventing thermal runaway and damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thermally conductive coating such as alumina is used, then thermal insulation is improved, but thermal expansion induced runaway events occur
Solution Approach 1:
The patent changes the thermal conductivity parameter of the coating by selecting alumina with specific properties and controlling its thickness, achieving a balance between thermal insulation and preventing thermal runaway events through optimized material parameters
Solution Approach 2:
The patent uses a composite coating system combining alumina ceramic with metallic bonds, creating a multi-layer structure that provides both thermal insulation and mechanical integrity while controlling thermal expansion effects
2Temperature
If a more insulative coating such as zirconia is used, then thermal insulation is improved, but coating spallation occurs during deep or high rate rub interactions
Solution Approach 1:
The patent employs composite material structures where alumina ceramic layers are bonded with metallic bonds, creating a composite system that combines the thermal insulation benefits of ceramic with the ductility and spallation resistance of metallic materials
Solution Approach 2:
The patent applies different material properties to different layers of the coating system, with the ceramic layer providing thermal insulation and the metallic bond layers providing mechanical strength and spallation resistance at the interface with the substrate
3Loss of energy
If the gap at tips of blades is set small to minimize leakage, then aerodynamic efficiency is improved, but blade tips rub against and engage the abradable seal causing potential damage
Solution Approach 1:
The patent designs the abradable seal as a sacrificial component that is intentionally made softer and more wear-resistant than the blade tips, allowing it to be consumed gradually during rub interactions while protecting the more valuable blade tips from damage
Solution Approach 2:
The patent applies a multi-layer coating system to the abradable seal that includes damping and energy-absorbing layers designed to cushion the impact and rub forces before they reach the substrate, preventing catastrophic failure
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 multi-layer coating system effectively prevents catastrophic thermal runaway events by reducing heat transfer and opening the gap between rotating and stationary parts during high rub interactions, ensuring efficient operation and reducing the risk of damage to the rotor shaft or casing.
Implementation Method 1
a ceramic layer, with a thickness of 7 mils to 12 mils (178 to 305 microns), on the metal bond coat providing thermal insulation of the surface
Implementation Method 2
being adapted to spall off upon high rub interaction
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An abradable coating (60;70) for interaction with tips of airfoils (such as vanes (26) or blades (28) of a compressor of a gas turbine engine) includes a metal bond coat (62;72), a ceramic layer (64;74), and an abradable layer (66;76). The ceramic layer on the metal bond coat provides insulation and acts as a fuse that is adapted to spall off upon high rub interaction. The abradable layer on the ceramic layer contacts the tips of the airfoils during operation of the compressor. The abradable layer is sufficiently abradable to roundup the coating by contact with the airfoil tips.