Abradable Coating Composition for CMAS-Resistant Turbine Rubs
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Solution Overview
Problem
Existing abradable coatings for gas turbine engines are susceptible to damage from blade tips due to high porosity, leading to permeability issues, CMAS infiltration, and reduced erosion resistance, while also being vulnerable to thermal spallation and corrosive forces.
Innovation Solution
An abradable coating with a matrix material comprising hafnon, zircon, or rare earth disilicates, and dislocator materials with Mohs hardness ≤6, having a porosity ≤10 vol.%, and a composition of 30-60% matrix and 40-70% dislocator materials, applied to ceramic matrix composites to enhance durability and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If high porosity (>20%) is provided in abradable coating to facilitate rub interaction with blade tip, then abradability is improved, but coating becomes permeable to CMAS infiltration and hot gas, and erosion resistance and thermal spallation resistance are reduced
Solution Approach 1:
The coating is designed with non-uniform porosity distribution, having higher porosity in the region that contacts the blade tip to facilitate abradability, and lower porosity in other regions to maintain resistance against CMAS infiltration and thermal spallation. This localized variation in porosity allows the coating to simultaneously satisfy both abradability requirements and durability requirements.
Solution Approach 2:
The abradable coating is formulated as a composite material system containing multiple phases including porous regions for abradability and denser regions for protection. The composite structure integrates materials with different porosity characteristics and mechanical properties to achieve both softness for blade tip interaction and sufficient strength for resisting environmental degradation.
2Strength
If abradable coating is made too hard to resist blade tip abrasion, then erosion resistance is improved, but damage to blade tips occurs during engine operation
Solution Approach 1:
The coating hardness parameter is carefully controlled to fall within an optimal range that is sufficiently soft to prevent blade tip damage while maintaining adequate erosion resistance. The patent specifies particular hardness values and ranges for the coating materials to achieve this balance, transforming the extreme option of 'too hard' to an optimized intermediate value.
Solution Approach 2:
The incorporation of porosity in the abradable coating reduces its effective hardness and makes it more compliant, allowing it to deform and absorb blade tip contact without causing damage while still providing sufficient erosion resistance through the porous structure's inherent energy absorption capabilities.
3Ease of operation
If porosity is increased to facilitate rub interaction, then abradability is improved, but permeability to corrosive hot gas and CMAS increases
Solution Approach 1:
The coating structure is designed with spatially varying porosity, where porous regions are localized to areas that contact the blade tip to enable abradability, while dense regions are positioned in areas exposed to hot gas and CMAS to prevent infiltration. This local differentiation resolves the contradiction between needing porosity for abradability and avoiding porosity for protection.
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 coating provides enhanced durability against blade tip abrasion, reduces permeability, and improves resistance to CMAS infiltration and thermal spallation, ensuring safer and more efficient engine operation.
Implementation Method 1
the blade tips act as an abrading component with respect to the abradable coating... the blade tips will abrade or cut into the abradable coating
Implementation Method 2
the resultant abradable coating is a significantly permeable coating which is susceptible to CMAS (Calcium-Magnesium-Aluminum-Silicate) infiltration... at high temperatures and potentially corrosive hot gas permeability
Data Source
AI summary
An abradable coating is described which comprises a matrix material selected from hafnon, mixtures of hafnon and zircon, and rare earth disilicates (RE2Si2O7), wherein RE is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu; and one or more dislocator materials selected from ceramic materials having a Mohs hardness of less than or equal to 6. The amount of matrix material is 30-60 vol. % based on the total volume of the coating excluding porosity, and the amount of dislocator materials is 40-70 vol. % based on the total volume of the coating excluding porosity. The abradable coating has a porosity of less than or equal to 10 vol. % based on the total volume of the abradable coating.