Ceramic Matrix Composite Surface Grading for FOD Resistance
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Solution Overview
Problem
Current ceramic matrix composites (CMCs) exhibit insufficient foreign object damage (FOD) resistance, particularly in rotating components like turbine blades, due to mismatched thermal expansion and elastic modulus between the CMC and its coatings, leading to stress formation and adhesion issues.
Innovation Solution
A method involving the application of an intumescent material onto the CMC preform, followed by heating to expand it, and densifying to form a ceramic matrix composite with expanded intumescent material in the voids between fiber tows, reducing local fiber volume fraction and improving filament distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If environmental barrier coatings are applied to CMCs to provide protection against harsh environmental conditions, then environmental resistance is improved, but thermal expansion and elastic modulus mismatches cause stress formation and adhesion problems
Solution Approach 1:
The patent applies a gradient structure to the interface layer between CMC and EBC, where the elastic modulus and thermal expansion properties gradually transition from the CMC side toward the EBC side. This local variation in material properties reduces stress concentration and prevents coating delamination while maintaining environmental protection.
Solution Approach 2:
The invention modifies the physical parameters (elastic modulus and thermal expansion coefficient) of the interface layer by creating a compositional gradient. This parameter change allows the interface to accommodate thermal expansion differences between CMC and EBC, reducing tensile stress during cooling and improving adhesion strength.
2Reliability
If CMCs use fiber toughening with interface materials to provide damage tolerance, then foreign object damage tolerance is improved, but FOD resistance remains below superalloy levels
Solution Approach 1:
The patent creates a composite interface layer combining ceramic fibers with matrix material in a graded structure. This composite approach provides both the damage tolerance of fiber toughening and the FOD resistance needed for rotating components, achieving performance above conventional CMCs but below superalloys.
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
Enhances FOD resistance by decreasing the local elastic modulus of the outer layers, minimizing damage from foreign objects and improving stress response, while maintaining strong adhesion with environmental barrier coatings.
Implementation Method 1
heating the coated ceramic matrix composite preform to expand the intumescent material
Implementation Method 2
applying a coating medium comprising intumescent material onto the outer layer (or layers) of a ceramic matrix composite preform
Data Source
AI summary
A method of reducing the local fiber volume fraction and improving the fiber/filament distribution within ceramic fiber tows located within the outer layers of a ceramic matrix composite (CMC) comprising depositing a coating medium containing intumescent material(s), such as in the form of a slurry containing intumescent particles, onto and into the outer layer of a ceramic matrix composite preform to alter the fiber structure of the surface of a ceramic matrix composite. The CMC loaded with intumescent material is heated to a temperature where the intumescent material expands, separating the filaments near the outside of the CMC and reducing local elastic modulus. After expansion, the ceramic matrix composite is subjected to densification and then, optionally, coated with an environmental barrier coating (EBC).