Direct-Bonded SiC/SiC EBC Coating to Prevent Delamination
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Solution Overview
Problem
Conventional environmental barrier coatings (EBCs) for ceramic matrix composites (CMCs) fail to withstand high temperatures and exhibit delamination due to thermal expansion mismatch and porosity, requiring bond coats that compromise mechanical stability and durability.
Innovation Solution
A direct bonding method forms an environmental barrier coating (EBC) with a transition layer integrally bonded to the SiC/SiC composite substrate using a rare earth silicate and sintering aid, eliminating the need for a bond coat and enhancing adhesion through in situ formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional EBCs based on rare earth disilicates are used, then environmental barrier protection is provided, but the coating decomposes above 2400°F forming porous monosilicate layer that exposes underlying EBC to exhaust gasses
Solution Approach 1:
The patent changes the chemical composition parameters of the EBC by incorporating reactive silicate glass formers (such as SiO2, B2O3, P2O5) alongside rare earth disilicates. This compositional modification allows the coating to maintain structural integrity and barrier properties at temperatures exceeding 2400°F by preventing the formation of porous monosilicate phases through controlled glass matrix formation.
Solution Approach 2:
The patent creates a composite EBC system by combining rare earth disilicates with reactive silicate glass formers and other ceramic powders. This composite approach leverages the high-temperature stability of rare earth disilicates while the glass-forming components create a dense, non-porous matrix that prevents decomposition and maintains barrier protection at elevated temperatures.
2Reliability
If conventional EBCs are applied, then environmental barrier function is achieved, but porosity develops that continuously exposes underlying EBC to exhaust gasses
Solution Approach 1:
The patent modifies the microstructural parameters of the EBC by incorporating glass-forming oxides that create a dense, vitrified matrix upon sintering. This glassy phase fills voids and pores, creating a continuous, non-porous structure that prevents gas penetration and eliminates the porosity issue inherent in conventional disilicate-based coatings.
Solution Approach 2:
The patent inverts the traditional approach by using glass-forming materials to deliberately create a non-porous, dense structure. The reactive silicates and glass formers undergo viscous flow and densification during sintering, eliminating porosity and creating a tight barrier that prevents exhaust gas penetration, thereby preventing material loss.
3Reliability
If conventional EBCs are applied, then coating protection is provided, but CTE differential causes stresses at coating interface during cyclic heating leading to delamination
Solution Approach 1:
The patent adjusts the thermal expansion parameters of the EBC by incorporating glass-forming materials with tunable CTE properties. The glass matrix can be compositionally adjusted to match the CTE of the CMC substrate, reducing thermal mismatch stresses during cyclic heating and preventing delamination while maintaining coating protection.
Solution Approach 2:
The patent creates a more homogeneous thermal expansion behavior by using a glass-based matrix that can be compositionally tailored to match the substrate's CTE. This homogenization of thermal properties across the coating-substrate interface reduces differential expansion stresses and improves interface stability during thermal cycling.
4Reliability
If conventional EBCs are applied, then environmental barrier is formed, but imperfect bonding with substrate leads to delamination
Solution Approach 1:
The patent changes the chemical and physical parameters of the EBC- substrate interface by using glass-forming materials that can chemically interact with the CMC substrate. The reactive glass components create strong chemical bonds and interfacial adhesion, transforming the weak physical bonding of conventional coatings into strong chemical bonding that prevents delamination.
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 method provides a spallation-resistant, high-temperature coating with improved environmental barrier protection and thermal insulation, reducing delamination and spallation, and maintaining mechanical integrity under steam exposure.
Implementation Method 1
heating the first layer to sinter the coating composition and thereby form an environmental barrier coating (EBC) adjacent the SiC/SiC composite substrate, and a transition layer integrally bonded to and between the SiC/SiC composite substrate and the EBC
Data Source
AI summary
A method of preparing a ceramic matrix composite (CMC) article is disclosed. The method includes depositing a first layer of a coating composition directly onto a surface of a silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite substrate, with the coating composition comprising a rare earth silicate and a sintering aid. The method also includes heating the first layer to sinter the coating composition to form an environmental barrier coating (EBC) adjacent the SiC/SiC composite and a transition layer integrally bonded to and between the substrate and the EBC. CMC articles prepared according to the method, including coated turbomachine components, are also disclosed.