Flexible Sublayer for Thermal Expansion Mismatch in Coated Composites
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Solution Overview
Problem
Current barrier coatings for polymer-matrix composites (PMCs) and high-temperature polymer-matrix composites (HTPMCs) fail to prevent thermo-oxidative degradation, oxygen diffusion, and thermal energy transfer, leading to reduced durability and lifespan, especially at elevated temperatures and in high-flow airstreams, due to mismatched coefficients of thermal expansion.
Innovation Solution
A dense barrier-coating system comprising a flexible sublayer and an oxygen-impervious barrier layer, either metallic or ceramic, that accommodates thermal expansion differences, preventing oxidation and reducing thermal energy transfer, thereby extending the lifespan of PMCs and HTPMCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic-based barrier coatings are used to protect PMCs and HTPMCs, then oxidation resistance is improved, but the coating cracks or spalls due to coefficient of thermal expansion mismatch
Solution Approach 1:
An intermediate layer is introduced between the ceramic-based barrier coating and the PMC/HTPMC substrate. This intermediate layer has a coefficient of thermal expansion that bridges the gap between the substrate and the ceramic coating, accommodating thermal expansion differences and preventing coating failure while maintaining oxidation protection.
Solution Approach 2:
The coating system is structured as a composite with multiple layers: the ceramic-based barrier coating layer provides oxidation resistance, while the intermediate layer provides mechanical compatibility. This composite structure combines the advantages of both materials while mitigating their individual disadvantages.
2Reliability
If metal-based barrier coatings are used to protect PMCs and HTPMCs, then oxidation resistance is improved, but the coating cracks or spalls due to coefficient of thermal expansion mismatch
Solution Approach 1:
An intermediate layer is introduced between the metal-based barrier coating and the PMC/HTPMC substrate. This intermediate layer has a coefficient of thermal expansion that bridges the gap between the substrate and the metal coating, accommodating thermal expansion differences and preventing coating failure while maintaining oxidation protection.
Solution Approach 2:
The coating system is structured as a composite with multiple layers: the metal-based barrier coating layer provides oxidation resistance, while the intermediate layer provides mechanical compatibility. This composite structure combines the advantages of both materials while mitigating their individual disadvantages.
3Reliability
If known oxygen-barrier coatings are used to prevent oxidation, then oxidation resistance is improved, but the coating cracks, spalls, or erodes at elevated temperatures
Solution Approach 1:
An intermediate layer is introduced between the oxygen-barrier coating and the PMC/HTPMC substrate. This intermediate layer accommodates coefficient of thermal expansion differences, allowing the oxygen-barrier coating to maintain adhesion and prevent oxidation even at elevated temperatures for extended periods.
Solution Approach 2:
The system changes the thermal expansion parameters by introducing an intermediate layer with appropriate thermal expansion properties. This allows the coating system to withstand elevated temperatures without cracking, spalling, or debonding, thereby extending the duration of service.
4Temperature
If ceramic-based barrier coatings are used to reduce temperature, then thermal protection is improved, but the coating does not adequately reduce temperature over long exposure times
Solution Approach 1:
The multi-layer composite coating system combines ceramic-based barrier coatings for thermal protection with an intermediate layer for mechanical stability. This structure maintains adequate temperature reduction over long exposure periods by preventing coating failure that would otherwise expose the substrate to the environment.
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 system provides enhanced durability, extended lifespan, reduced temperature, and weight savings for PMCs and HTPMCs, enabling their use in high-temperature environments with improved resistance to cracking, spalling, and erosion, while reducing the need for insulation materials.
Implementation Method 1
accommodating differences in coefficients of thermal expansion (CTEs) to prevent the coating from cracking, separating, or debonding from the substrate at elevated temperatures
Implementation Method 2
an oxygen-impervious, dense barrier-coating layer... prevents oxygen ingression into the PMC or HTPMC to prevent oxidation
Implementation Method 3
reduces thermal energy transfer to the PMC or HTPMC substrate to reduce nominal substrate temperature
Data Source
AI summary
A method of making a coated polymer-matrix composite (PMC) having high-temperature oxidation protection includes bonding a first surface of a flexible sublayer that is free of water to a first surface of a dry PMC substrate having a first coefficient of thermal expansion. The flexible sublayer includes an electrically conductive material in an effective amount to enable electrical conductivity of the flexible sublayer, and includes a low-modulus-of-elasticity material. The method includes heating the bonded flexible sublayer and the PMC substrate, and bonding a first surface of an oxygen-impervious, dense barrier-coating layer to a second surface of the flexible sublayer to form the coated PMC having high-temperature oxidation protection. The dense barrier-coating layer includes metallic materials and ceramic materials, each having a respective second coefficient of thermal expansion, and flexibility of the flexible sublayer protects the respective bonds when the first and second coefficients of thermal expansion are unequal.