Abradable Coating Fine Pores Gas Turbine Seal
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Solution Overview
Problem
Existing porous metal seals in gas turbine engines suffer from high gaseous permeability due to large pore sizes, leading to aerodynamic efficiency losses through air leakage, which current thermally sprayed abradable seals fail to adequately address.
Innovation Solution
A method of forming a low-density porous metal coating by co-depositing nickel aluminum alloy or MCrAlY metal matrix particles with metal precursor compound particles, followed by heat treatment in a cracked ammonia atmosphere to create a coating with interconnected pores of 2-25 microns, reducing permeability and enhancing erosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If porous metal seal coatings are made with larger pores to enhance abradability, then the seal material becomes easier to wear and form mating surfaces, but gaseous permeability increases causing air leakage and aerodynamic efficiency losses
Solution Approach 1:
The patent changes the pore size parameter from conventional large pores (typically >50 microns) to fine pores (2-25 microns) while maintaining high porosity (40-80% volume percent). This parameter change reduces gaseous permeability and air leakage while preserving abradability, directly resolving the contradiction between ease of operation and energy loss.
Solution Approach 2:
The patent uses a porous metal matrix structure with fine interconnected pores formed by co-depositing metal particles with organic binder particles that are subsequently removed. The porous structure provides abradability for seal formation while the fine pore size (2-25 microns) minimizes gaseous permeability, allowing the material to simultaneously achieve both required properties.
2Ease of operation
If the seal coating is made more porous to improve abradability and reduce density, then the seal material wears more easily to generate optimized mating surfaces, but the structural strength and erosion resistance decrease
Solution Approach 1:
The patent creates a composite structure by co-depositing metal matrix particles with organic binder particles, then removing the binder to form a porous metal structure. The metal matrix provides strength and erosion resistance while the controlled porosity (40-80% volume percent with 2-25 micron pores) provides abradability, resolving the contradiction between strength and ease of operation.
Solution Approach 2:
The patent achieves different properties at different scales: at the macro scale, the high porosity (40-80% volume percent) provides abradability and low density; at the micro scale, the fine pore size (2-25 microns) and metal matrix structure provide strength and erosion resistance. This local quality differentiation resolves the contradiction between abradability and strength.
3Ease of manufacture
If conventional fugitive polymer particles are used to create porosity through decomposition, then the coating becomes porous and abradable, but the decomposition products vent through interconnected porosity creating large pores that increase gaseous permeability
Solution Approach 1:
The patent changes the pore size parameter from large pores (typically >50 microns) created by conventional polymer decomposition to fine pores (2-25 microns) by controlling the decomposition process and metal particle infiltration. This parameter change reduces gaseous permeability while maintaining porosity, directly resolving the contradiction between ease of manufacture and energy loss.
Solution Approach 2:
The patent uses metal particles as an intermediary during the porosity formation process. The metal particles infiltrate the spaces between decomposing polymer particles and form the final pore walls after polymer removal. This intermediary role of metal particles allows control over pore size and structure, creating fine pores that reduce air leakage while maintaining manufacturability.
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 resulting coating effectively minimizes air leakage by reducing pore size and increasing the strength of the seal, improving the thermal efficiency of gas turbine engines while maintaining abradability to prevent blade damage.
Implementation Method 1
heat treating the structure to form a porous coating on the structure, wherein the metal precursor compound particles decompose during heat treatment to leave fine pores with metal walls
Implementation Method 2
thermal spraying metal matrix particles and metal precursor compound particles to co-deposit the metal matrix particles and metal precursor compound particles on the structure
Implementation Method 3
heat treating the structure comprises heating the structure to 700°C (1292°F) for 2 hours in a cracked ammonia atmosphere
Data Source
Figure 1
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AI summary
A low density abradable coating (60;70) for use as a seal material is formed by depositing a metal bond coat followed by depositing a low density, porous, abradable metal seal layer (64;74) on the bond coat. The seal layer is formed by co-depositing metallic sponge particles and metal precursor particles. The metal precursor particles decompose during heat treatment leaving fine pores distributed throughout the microstructure.