Ceramic Heat Shield Infiltration for Corrosion Resistance
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Solution Overview
Problem
Ceramic heat shields in gas turbines face corrosion and erosion due to the conversion of mullite to secondary corundum under high temperatures, leading to premature coating failure and reduced service life, with existing aluminum oxide coatings exhibiting adhesion issues and limited durability.
Innovation Solution
A porous ceramic heat shield with an infiltration coating of yttrium aluminum garnet (YAG) is applied to close surface pores, preventing hot gas invasion and corrosion, while maintaining elongation tolerance and allowing for improved adhesion of additional coatings, using a method that involves immersing the ceramic body in a YAG-containing suspension under vacuum and subsequent firing to achieve deep penetration and crystalline integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum oxide coating is applied to protect ceramic heat shields from corrosion, then corrosion resistance is improved, but adhesion to the ceramic surface deteriorates
Solution Approach 1:
The patent introduces a transition layer comprising aluminum oxide and mullite between the aluminum oxide coating and the mullite ceramic substrate. This intermediate layer serves as a mediator that provides both corrosion resistance and strong adhesion to the substrate, resolving the contradiction between protection and bonding strength
Solution Approach 2:
The protective system uses composite material structure with multiple layers: aluminum oxide coating, transition layer (aluminum oxide + mullite), and mullite substrate. This composite structure combines the corrosion resistance of aluminum oxide with the adhesion benefits of mullite, achieving both requirements simultaneously
2Manufacturing precision
If slurry spray method is used to apply aluminum oxide coating, then coating fineness is improved, but post-sintering cracks and premature sanding occur
Solution Approach 1:
The patent applies plasma spraying instead of slurry spray, fundamentally changing the coating application method parameters. This produces a coating with different microstructure and bonding characteristics that avoids post-sintering cracks and premature sanding while maintaining appropriate fineness
3Manufacturing precision
If flame spray method is used to apply aluminum oxide coating, then coating density is improved, but coating becomes brittle and cannot follow deformations
Solution Approach 1:
The patent uses plasma spraying instead of flame spraying, changing the thermal processing parameters. This produces a coating with appropriate density while maintaining flexibility through controlled microstructure and bonding, allowing the coating to follow substrate deformations without becoming brittle
4Adaptability or versatility
If porous ceramic structure is used to preserve elongation tolerance, then deformation capability is improved, but corrosion and erosion attacks increase
Solution Approach 1:
The patent segments the ceramic structure into two distinct zones: a dense surface layer (infiltration layer) that resists corrosion and erosion, and an inner porous structure that provides elongation tolerance. This segmentation allows each zone to fulfill its specific function without compromise
Solution Approach 2:
The patent applies local quality by creating a dense infiltration layer only at the surface where corrosion and erosion occur, while maintaining porosity in the interior where elongation tolerance is needed. This localized treatment optimizes protection where required without sacrificing overall deformation capability
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 YAG infiltration coating significantly extends the service life of ceramic heat shields by reducing erosion and particle release, minimizing damage to turbine blades, and enabling protection of lateral faces without altering the heat shield dimensions, while ensuring thermal shock stability and uniform coating application.
Implementation Method 1
the infiltration of a highly porous ceramic surface it is achieved that the porosity of the ceramics on the surface is significantly reduced and corrosive products thus cannot invade
Implementation Method 2
the porosity of the ceramics on the surface is significantly reduced
Implementation Method 3
immersing the ceramic body in a YAG-containing suspension under vacuum and subsequent firing to achieve deep penetration
Implementation Method 4
subsequent firing to achieve deep penetration and crystalline integration
Data Source
AI summary
An improved ceramic heat shield for a gas turbine is provided. The ceramic heat shield has a porous ceramic body and according to the embodiments an infiltration coating that is provided in a surface layer of the porous ceramic body and contains an infiltration coating material designed to gas-tightly seal pores of the ceramic body.