SiC Ceramic Overcoating for Carbon-Carbon Brake Oxidation
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Solution Overview
Problem
Carbon-carbon composite brake discs, including carbon-carbon-silicon carbide composites, face oxidation issues at elevated temperatures, leading to degradation of mechanical properties, and existing silicon carbide coatings are prone to cracking or peeling due to weak bonds between layers.
Innovation Solution
A low-cost silicon carbide ceramic overcoating system using sub-micron size silicon carbide particles, water-miscible silicate binders, and pH modifiers is applied, which does not require high-temperature curing and forms a strong bond with the underlying layers, providing a protective barrier against oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphoric acid-based penetrants are used to protect carbon-carbon composite brake discs against oxidation, then oxidation resistance is improved, but the coating degrades at peak operating conditions
Solution Approach 1:
The patent applies a multi-layer composite coating system consisting of a phosphoric acid-based penetrant layer combined with a silicon carbide ceramic overcoating. This composite structure leverages the oxidation resistance of phosphoric acid penetrants while adding the high-temperature stability of SiC ceramic to prevent degradation at peak operating conditions.
Solution Approach 2:
The protective coating is segmented into multiple functional layers: the phosphoric acid-based penetrant layer provides oxidation resistance, while the separate silicon carbide ceramic overcoating layer provides high-temperature structural stability. This segmentation allows each layer to perform its specific function optimally without compromising the other.
2Reliability
If silicon carbide coating is applied to protect against oxidation, then oxidation resistance is improved, but the coating cracks or peels due to weak bond between layers
Solution Approach 1:
The patent introduces a carbon interlayer as an intermediary between the carbon-carbon composite substrate and the silicon carbide coating. This intermediate layer improves adhesion and prevents cracking or peeling by providing a transition zone that accommodates thermal expansion differences and creates stronger bonding interfaces.
Solution Approach 2:
The multi-layer composite structure including the carbon interlayer, silicon carbide coating, and phosphoric acid penetrant creates a system where each material complements the others. The carbon interlayer specifically addresses the bonding issue by creating a gradient transition that strengthens the interface between dissimilar materials.
3Reliability
If high-temperature curing is used to form silicon carbide coating, then coating integrity is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent modifies the curing parameters by using a lower curing temperature regime combined with the phosphoric acid-based penetrant system. This parameter change allows the silicon carbide coating to form with adequate integrity at reduced temperatures, simplifying the manufacturing process while maintaining coating quality.
Solution Approach 2:
The phosphoric acid-based penetrant acts as a chemical intermediary that facilitates coating formation at lower temperatures. It creates a reactive surface layer that enables silicon carbide deposition and bonding without requiring extreme thermal conditions, thus reducing manufacturing complexity.
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 effectively protects carbon-carbon composite brake discs from oxidation, maintaining structural integrity and mechanical properties under extreme conditions without the need for high-temperature curing, making it suitable for aerospace applications like aircraft braking systems.
Implementation Method 1
The ceramic overcoating composition... forms a strong bond with the underlying layers
Implementation Method 2
providing a protective barrier against oxidation
Data Source
AI summary
Coated article, e.g., a brake disc, comprising a carbon-carbon composite component or a carbon-carbon-silicon carbide component coated at least with a phosphorus-containing antioxidant undercoating, the undercoating being covered by a silicon carbide particle-containing overcoating of alkali or alkaline earth metal silicate, pH modifier, and silicon carbide particles. Also, method of protecting a carbon-carbon composite brake disc or a carbon-carbon-silicon carbide composite brake disc against oxidation, by: coating the composite brake disc with a first phosphoric acid-based penetrant system; curing the penetrant coating at a temperature of 200° C. or above to form a first coating on the composite brake disc; applying the ceramic coating composition of claim 1 over the first coating and curing the ceramic coating at a temperature below 200° C. to form a second coating on the composite brake disc; and optionally coating the coated composite brake disc so obtained with a second phosphoric acid-based penetrant system; and curing the penetrant coating at a temperature of 200° C. or above to form a third coating on the composite brake disc.