SiC-Coated Carbon Composite Thermal Stress Relief
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Solution Overview
Problem
SiC-coated graphite materials face issues with warpage and strength due to high porosity requirements for ceramic coating deposition, leading to compromised thermal shock resistance and dimensional accuracy.
Innovation Solution
A SiC-coated carbon composite material with a graphite base material porosity of 12-20% and a CVD-SiC coating, featuring a SiC-infiltrated layer with stepwise decreasing Si content from the surface to the base material, which relieves thermal expansion stress and enhances bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the porosity of the graphite base material is increased to allow SiC deposition, then the ceramic coating can be formed, but the strength of the graphite base material decreases
Solution Approach 1:
The patent optimizes the porosity parameter of the graphite base material to a specific range (12-20%) to balance SiC deposition capability and structural strength. This parameter change allows the material to maintain sufficient strength while still enabling effective ceramic coating formation through the porous structure.
Solution Approach 2:
The patent utilizes the porous structure of the graphite base material as a key feature. The controlled porosity (12-20%) serves as both a structural characteristic that maintains strength and a functional property that enables SiC coating infiltration and bonding, eliminating the need to choose between the two conflicting requirements.
2Reliability
If the occupancy rate of SiC in the surface layer is increased to 15-50% to obtain anchoring effect, then thermal shock resistance improves, but warpage increases due to thermal expansion difference
Solution Approach 1:
The patent creates different SiC occupancy rates at different depths of the graphite base material. The surface layer has higher SiC occupancy (15-50%) for anchoring and thermal shock resistance, while deeper regions have lower occupancy to reduce thermal expansion differences and minimize warpage. This local variation in composition resolves the contradiction between thermal shock resistance and dimensional accuracy.
3Quantity of substance
If the thickness of the ceramic composite material is reduced, then material usage decreases, but dimensional accuracy worsens due to warpage
Solution Approach 1:
The patent changes the compositional parameters of the graphite base material, specifically optimizing porosity (12-20%) and creating a depth-dependent SiC occupancy profile. These parameter changes enable the material to maintain dimensional accuracy even when the overall thickness is reduced, as the controlled SiC distribution minimizes thermal expansion differences that cause warpage.
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 solution provides improved strength, reduced warpage, and enhanced thermal shock resistance while maintaining dimensional accuracy and preventing exfoliation of the CVD-SiC coating.
Implementation Method 1
a SiC coating is formed on a surface of the graphite by a CVD method
Implementation Method 2
there is a concern that as the thickness of the ceramic composite material having a ceramic coating on its surface is thinner, the dimensional accuracy becomes worse
Data Source
AI summary
Provided is a SiC-coated carbon composite material including a graphite base material and a CVD-SiC coating covering the graphite base material. A porosity of a core part of the graphite base material is 12 to 20%, and a SiC-infiltrated layer extending from the CVD-SiC coating is included in a periphery of the core part of the graphite base material. The SiC-infiltrated layer is constituted of a plurality of regions arranged such that Si content becomes smaller stepwise in an order from a first surface on the CVD-SiC coating side toward a second surface on the graphite base material side.