SiC Matrix Composite Oxidation Resistance via Layered Silicate Barriers
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Solution Overview
Problem
SiC/SiC ceramic matrix composites used in gas turbine engines suffer from active oxidation due to the instability of silicon dioxide at high gas velocities and pressures, leading to component recession and potential failure.
Innovation Solution
A method involving the deposition of alternating layers of silicon carbide (SiC) and silicon carbonitride (SiCN) or silicon nitride (Si3N4) doped with elements like yttrium, ytterbium, or dysprosium, which form stable high-temperature silicates, along with an optional interface layer of boron nitride or pyrolytic carbon, to prevent oxidation through chemical vapor infiltration and subsequent processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If SiC/SiC ceramic matrix composites are used in gas turbine engines, then high temperature mechanical and physical properties are improved, but active oxidation resistance deteriorates due to silicon dioxide instability
Solution Approach 1:
The patent applies composite materials by combining SiC matrix with doped Si3N4 layers containing rare earth elements (Y, Yb, Dy, etc.). This composite structure creates a layered architecture where the doped Si3N4 layers form stable silicate glass phases upon oxidation, preventing further oxygen penetration to the SiC matrix, thus resolving the contradiction between high-temperature capability and oxidation resistance
Solution Approach 2:
The patent implements local quality by doping specific regions (Si3N4 layers) with rare earth elements to create localized oxidation-resistant zones. The doped layers are positioned at strategic locations within the composite structure to form protective barriers, while the bulk SiC matrix maintains its high-temperature mechanical properties, allowing different regions to fulfill different functional requirements
2Reliability
If alternating layers of SiC and doped Si3N4 are deposited by CVI, then oxidation resistance is improved through stable silicate formation, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the matrix composite into alternating layers of SiC and doped Si3N4. This layered segmentation allows each layer to perform its specific function: SiC layers provide structural integrity and high-temperature strength, while doped Si3N4 layers provide oxidation protection. The segmentation is achieved through controlled CVI deposition processes
Solution Approach 2:
The patent utilizes parameter changes by modifying the chemical composition of Si3N4 through rare earth element doping during CVI deposition. By controlling doping concentrations and deposition parameters, the material transforms to form stable silicate glass phases upon oxidation, changing from a potentially harmful oxidation product to a protective barrier, thus improving oxidation resistance
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 formed ceramic matrix composite exhibits enhanced oxidation resistance by creating effective barriers to oxygen and steam diffusion, thereby reducing component recession and extending the operational lifespan of gas turbine engine components.
Implementation Method 1
On contact with oxygen the BN coating is oxidised to form a boron oxide and/or boron silicate glass layer. This layer prevents further oxidation of the underlying material.
Implementation Method 2
the instability of silicon dioxide (SiO2) when exposed to the high gas velocity and pressures of the engine environment. The doped Si3N4 layer forms a stable silicate glass upon oxidation
Implementation Method 3
The matrix layers are deposited by chemical vapor infiltration
Data Source
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AI summary
Ceramic matrix composites include a fiber network and a matrix including layers of first and second materials. The first material may include SiC. The second material may include an element that when oxidized forms a silicate that is stable at high temperatures.