Mullite NOSC Bondcoat for High-Temperature EBC Oxidation
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Solution Overview
Problem
Current environmental barrier coatings (EBCs) for ceramic components, such as silicon carbide and silicon nitride, face limitations due to the low melting point of silicon bondcoats, which restrict operational temperatures and lead to delamination at high temperatures, causing blistering and spallation due to oxygen penetration and carbonaceous/nitrous oxide gas accumulation.
Innovation Solution
A mullite/NOSC bondcoat is introduced, comprising a non-oxide silicon ceramic phase within a mullite phase, with a volume ratio of 60% to 95% mullite and 5% to 40% NOSC, which acts as a sacrificial layer to prevent oxygen penetration and allow gaseous oxides to escape, thereby preventing substrate oxidation and extending the operational temperature limit to 1650 °C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon bondcoat is used to prevent substrate oxidation, then oxidation resistance is improved, but the operational temperature limit is reduced due to low melting point
Solution Approach 1:
The patent applies composite materials by combining mullite (a high-temperature stable ceramic) with silicon carbide particles to create a bondcoat composite. This composite structure allows the coating to maintain oxidation protection through silicon carbide while the mullite matrix provides high-temperature structural stability up to 1650°C, resolving the contradiction between oxidation resistance and temperature limit.
Solution Approach 2:
The patent changes the fundamental material parameter from pure silicon (melting point 1414°C) to a mullite-silicon carbide composite system. This parameter change in material composition transforms the melting behavior, eliminating the low-temperature melting issue while preserving oxidation protection mechanisms through controlled silicon carbide oxidation.
2Object-affected harmful factors
If a dense EBC is used to seal out water vapor, then recession resistance is improved, but oxygen penetration occurs causing blistering and spallation
Solution Approach 1:
The patent applies porous materials by incorporating controlled porosity into the EBC structure. This porous architecture allows gaseous oxidation products (CO, CO2, NO, NO2) to escape through the coating without building up pressure that would cause blistering, while the overall dense structure maintains water vapor seal. The porosity resolves the contradiction between recession protection and gas venting.
Solution Approach 2:
The patent uses the mullite bondcoat as an intermediary layer between the substrate and EBC. This intermediate layer serves as a controlled oxidation zone where gaseous products can form and escape laterally through the porous EBC, preventing the harmful accumulation that would otherwise cause blistering and spallation of the outer coating.
3Reliability
If the EBC structure is made more complex to prevent blistering, then reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the chemical composition parameters of the bondcoat (mullite with silicon carbide particles) to inherently provide blistering resistance. This compositional parameter change creates a system where controlled oxidation and gas escape occur naturally through the material properties, eliminating the need for complex multi-layer EBC structures designed specifically to prevent blistering.
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 mullite/NOSC bondcoat effectively prevents substrate oxidation, allows gaseous oxides to vent, and maintains structural integrity, reducing blistering and spallation, thus enabling higher operational temperatures without delamination, making it suitable for high-temperature applications like gas turbine engines.
Implementation Method 1
The carbonaceous (i.e., CO, CO 2 ) or nitrous (i.e., NO, NO 2 , etc.) oxide gases cannot escape out through the dense EBC and thus, blisters form
Implementation Method 2
The carbonaceous (i.e., CO, CO 2 ) or nitrous (i.e., NO, NO 2 , etc.) oxide gases cannot escape out through the dense EBC
Implementation Method 3
The silicon bondcoat provides a layer that oxidizes (forming a passive silicon oxide layer beneath the EBC) without liberating a gaseous by-product
Implementation Method 4
a mullite/NOSC bondcoat on the surface of the substrate... extending the operational temperature limit to 1650 °C
Data Source
Figure 1~2
Figure 3
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AI summary
A coated component (100), along with a method of making the same, is provided. The coated component (100) includes a ceramic matrix composite (CMC) substrate (102) comprising silicon carbide and having a surface (103); a mullite/nosc bondcoat (104) on the surface (103) of the substrate (102); and an environmental barrier coating on the mullite/nosc bondcoat (104). The mullite/nosc bondcoat (104) comprises a non-oxide silicon ceramic (NOSC) phase contained within a mullite phase (112), with the mullite/nosc bondcoat (104) comprising 60% to 95% by volume of the mullite phase (112), such as 65% to 93% by volume of the mullite phase (112).