Turbine Abradable Coating Chemistries for CMC Oxidation Resistance
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Solution Overview
Problem
Existing abradable coatings in gas turbine engines face issues such as porosity providing pathways for oxygen penetration and molten contaminant infiltration, leading to potential substrate compromise and cracking, especially when used with ceramic matrix composite substrates, and traditional dislocators like hBN are ineffective at high temperatures.
Innovation Solution
Incorporating fillers like alkaline earth or transition metal tungstates, molybdates, and rare earth phosphates as dislocators in the abradable coating, which have lower shear strength than the matrix, reducing porosity and enhancing abradability while maintaining structural stability at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If porosity is increased to achieve abradability, then wear resistance is improved, but oxygen penetration and molten contaminant infiltration increase compromising substrate bonding
Solution Approach 1:
The patent uses controlled porosity in the abradable coating to enable wear resistance while managing the trade-off with substrate bonding. The coating is designed with specific porosity levels that allow abrasion while limiting harmful penetrations.
Solution Approach 2:
The patent employs composite material structures combining ceramic matrix with controlled porosity and potential filler phases to achieve both abradability and protection against oxygen and molten contaminant infiltration, resolving the contradiction between wear resistance and substrate bonding integrity.
2Strength
If traditional hBN dislocator is used in abradable coating, then abradability is maintained, but oxidation/volatilization resistance is poor at temperatures above 1800°F
Solution Approach 1:
The patent changes the chemical composition parameters of the dislocator material from traditional hBN to alternative chemistries that maintain low shear strength for abradability while providing superior oxidation and volatilization resistance at high temperatures above 1800°F.
Solution Approach 2:
The patent develops composite coating systems incorporating alternative dislocator materials that combine the desired mechanical properties for abrasion resistance with enhanced thermal stability and oxidation resistance, replacing hBN with materials suitable for high-temperature turbine environments.
3Strength
If YSZ coating is applied to CMC substrate, then abradability is achieved, but CTE mismatch causes cracking and spallation during operation
Solution Approach 1:
The patent changes the coating material composition from YSZ to alternative ceramic chemistries with coefficients of thermal expansion matched to CMC substrates, eliminating CTE mismatch and preventing cracking and spallation while maintaining abradability through controlled porosity and dislocator phases.
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 proposed dislocator chemistries reduce the risk of substrate degradation and cracking by minimizing porosity and improving abradability, ensuring durability and effectiveness in high-temperature turbine environments.
Implementation Method 1
A dislocator may fill porosity in the matrix while not compromising abradability
Implementation Method 2
the hBN dislocator prevents sintering of the matrix and is softer than the matrix so as to deform under shear
Implementation Method 3
the hBN dislocator prevents sintering of the matrix
Data Source
AI summary
A coated article (20;60) includes a substrate (22) and a coating (24;62) on the substrate. The coating includes at least a first layer (30). The first layer has: a matrix (50); and a filler (52) at 2.0% to 40% by volume in the first layer. The first layer is selected from alkaline earth or transition metal (M) tungstates (MWO4); alkaline earth molybdates (MMoO4); rare earth (RE) phosphates (REPO4); and combinations thereof.