CMC Article Densification via Carbon-Silicon Infiltration
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Solution Overview
Problem
Ceramic matrix composite (CMC) articles, particularly those made using the polymer infiltrated and pyrolysis (PIP) method, suffer from high residual porosity due to voids that cannot be fully filled, leading to weakness and susceptibility to oxidation and humidity, limiting their durability in high-temperature applications like gas turbine engines.
Innovation Solution
A method involving pyrolyzing a CMC article at 1000-1400 °C, coating pores with carbon, pyrolyzing the carbon to form carbon pores, and then coating these pores with silicon to react with the existing silicon carbide matrix, thereby densifying the article through multiple infiltration and pyrolysis cycles, while using a silicon carbide precursor resin with fillers like silicon, boron carbide, or silicon nitride to achieve high density and reduce porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple PIP cycles are used to reduce residual porosity, then porosity reduction is achieved, but some voids become sealed off and infiltration cycles can no longer fill them, limiting further densification
Solution Approach 1:
The patent applies preliminary action by coating the fiber preform with pyrolytic carbon and silicon carbide before the PIP process, and by sealing pores with carbon before the final silicon infiltration. This preliminary coating prevents resin penetration into fibers during PIP cycles, ensuring that voids remain accessible for subsequent silicon infiltration to achieve densification.
Solution Approach 2:
The patent uses carbon as an intermediary material. Carbon is deposited on the fiber preform and used to seal pores temporarily during the PIP process, then carbonized to form a stable barrier. This intermediary carbon layer allows the process to proceed in stages, enabling subsequent silicon infiltration to fill voids without resin contamination.
2Ease of manufacture
If PIP based CMC articles are produced with high porosity to allow infiltration cycles, then infiltration can proceed, but the resulting articles are weak and susceptible to oxidation and humidity
Solution Approach 1:
The patent applies local quality by creating different pore structures in different regions of the material. The fiber preform is coated with pyrolytic carbon to create sealed, non-porous regions that prevent resin infiltration, while controlled voids are maintained in other areas for silicon infiltration. This localized pore management allows the material to achieve both infiltration capability and environmental resistance.
Solution Approach 2:
The patent creates a composite structure with multiple phases: pyrolytic carbon coating on fibers, silicon carbide matrix from PIP cycles, and silicon infiltrant in the voids. This multi-phase composite structure provides both the infiltration pathways needed during manufacturing and the dense, environmentally resistant structure needed for final performance.
3Manufacturing precision
If full densification is achieved through multiple infiltration cycles, then porosity is reduced, but the process becomes costly and inefficient
Solution Approach 1:
The patent applies partial action by performing only the necessary number of PIP cycles to achieve initial matrix formation, rather than continuing until complete densification. The pyrolytic carbon coating is applied once before PIP cycles to establish the pore structure, and silicon infiltration is performed once after PIP to achieve final densification. This partial cycling approach achieves sufficient densification without the excessive manufacturing time and cost of multiple complete cycles.
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 effectively reduces porosity and enhances mechanical properties and environmental resistance of CMC articles, improving their durability and performance in high-temperature environments without the need for full densification, which is costly and inefficient.
Implementation Method 1
The polymer is heated, and at high temperatures, the polymer pyrolyzes into a ceramic matrix, such as silicon carbide, silicon nitride, or into a carbon matrix.
Implementation Method 2
The carbon is pyrolyzed at a temperature of 1000-1800 °C.
Implementation Method 3
melting the metal silicon powder in a vacuum atmosphere and then diffusing the molten metal silicon powder into the primarily reaction-sintered fiber composite material
Data Source
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AI summary
A method of densifying a CMC article includes the steps of pyrolyzing a CMC article until a desired initial porosity is achieved, coating CMC pores within the CMC article with carbon, pyrolyzing the carbon to form carbon pores, coating the carbon pores with silicon, and heat treating the CMC article to create a silicon carbide filled pore integrated with silicon carbide of the CMC article to densify the CMC article.