High Purity Ceramic Abradable Coatings for Gas Turbine Engines
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Solution Overview
Problem
Current abradable thermal barrier coatings for gas turbine engines face challenges in achieving high-temperature stability, porosity levels, and wear resistance, leading to inefficiencies and potential damage due to mismatched expansion coefficients and sintering issues.
Innovation Solution
A high purity zirconia and/or hafnia-based ceramic coating system with a superalloy substrate and oxidation-resistant bond coat, incorporating a fugitive material for increased porosity and sintering resistance, applied using thermal spray methods to achieve a balanced microstructure and reduced blade wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional YSZ coatings are used to provide thermal insulation, then thermal barrier function is achieved, but sintering resistance is insufficient leading to microstructure degradation at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the YSZ coating by strictly controlling impurity levels (SiO2 < 0.05 wt%, Al2O3 < 0.05 wt%, Na2O < 0.02 wt%, Fe2O3 < 0.02 wt%, TiO2 < 0.02 wt%, CaO < 0.02 wt%, MgO < 0.02 wt%) to enhance sintering resistance and maintain microstructure stability at high service temperatures above 1000°C
Solution Approach 2:
The patent creates a composite coating system consisting of high-purity YSZ top coat combined with specific bond coat materials (MCrAlY or NiCrDS alloys), where the bond coat provides oxidation resistance and thermal expansion matching while the YSZ layer provides thermal insulation with improved sintering resistance
2Loss of energy
If ceramic abradable coating is applied to reduce gas leakage, then sealing efficiency is improved, but coating wear and blade wear increase under high stress conditions
Solution Approach 1:
The patent optimizes the mechanical properties of the YSZ coating by controlling its microstructure (porosity 5-20%, crack density) and composition to achieve the right balance between abradability for sealing and wear resistance to prevent excessive material loss during operation
Solution Approach 2:
The patent creates different local properties within the coating system: the YSZ top coat has specific porosity and crack characteristics for abradability, while the bond coat has different composition and properties for adhesion and oxidation resistance, with each layer optimized for its specific function
3Use of energy by stationary object
If coating thickness is increased to improve thermal insulation, then thermal barrier performance is enhanced, but thermal expansion mismatch causes stress and potential delamination
Solution Approach 1:
The patent creates a graded structure where the bond coat has intermediate thermal expansion properties between the substrate and the YSZ top coat, with each layer having optimized thickness and composition to manage thermal stress locally, allowing the YSZ layer to be sufficiently thick for insulation without causing delamination
Solution Approach 2:
The patent selects bond coat materials (MCrAlY or NiCrDS alloys) with thermal expansion coefficients that bridge the gap between the superalloy substrate and the YSZ coating, reducing thermal expansion mismatch stress in the thick coating system
4Ease of operation
If high porosity is introduced to improve abradability, then sealing performance is enhanced, but structural integrity and erosion resistance decrease
Solution Approach 1:
The patent introduces a controlled porous microstructure (5-20% porosity) in the YSZ top coat to improve abradability and sealing performance, while the porous structure is designed with specific pore size, distribution, and connectivity to maintain sufficient structural integrity and erosion resistance
Solution Approach 2:
The patent creates a composite structure where the porous YSZ top coat provides abradability and the denser bond coat layer provides structural support and erosion resistance, with the two layers working together to achieve both sealing performance and durability
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 service lifetime of gas turbine engines by maintaining a stable microstructure and reducing thermal conductivity, thereby enhancing operational efficiency and temperature tolerance while minimizing blade wear and leakage.
Implementation Method 1
applied using thermal spray methods
Implementation Method 2
incorporating a fugitive material for increased porosity
Implementation Method 3
reducing thermal conductivity, thereby enhancing operational efficiency and temperature tolerance
Implementation Method 4
maintaining a stable microstructure... reducing blade wear and leakage... sintering issues
Data Source
AI summary
The invention is directed to a material and method for obtaining a ceramic abradable system for high temperature applications. High purity partially stabilized zirconia and/or hafnia base material has higher sintering resistance compared to conventional 6-9 weight percent yttria stabilized zirconia systems. The benefits of these systems are higher service lifetime and low thermal conductivity to achieve high operating temperatures. System includes a superalloy substrate, oxidation resistant bond coat and a thick ceramic abradable top coat. Total coating thickness is about 0.5-5 mm. In some applications an intermediate layer of high purity partially stabilized zirconia or a partially stabilized YSZ/MCrAlY cermet is applied over the oxidation resistant bond coat. In other applications an abradable system is applied on top of a grid. Additional benefits should be reduced blade wear at high operating conditions.