Conforming Reflective Layer for Gas Turbine Thermal Barrier Coatings
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Solution Overview
Problem
High-temperature gas turbine engines face significant heat transfer issues due to thermal radiation through ceramic thermal barrier coatings, which can contribute more to overall heat transfer than convective processes, especially at elevated temperatures and high combustor pressures.
Innovation Solution
A conforming reflective layer made from platinum group metals is applied via atomic layer deposition, penetrating up to 20 times deeper than the gap opening of the porous microstructure of the ceramic coating without physical contact with the substrate, to reduce radiation heat transport. This layer conforms to the porous features of the ceramic coating and is formed from materials like platinum, palladium, or rhodium, ensuring optical opacity and resistance to oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a ceramic thermal barrier coating is used to insulate hot section components, then component durability and survival at higher temperatures are improved, but radiation heat transfer through the coating increases at elevated temperatures
Solution Approach 1:
A metallic reflective layer is introduced as an intermediary between the ceramic thermal barrier coating and the hot section component. This reflective layer specifically targets and reflects thermal radiation before it can be absorbed by the component, while the ceramic coating continues to provide thermal insulation. The reflective layer acts as a mediator that addresses the radiation heat transfer issue without compromising the thermal barrier function.
Solution Approach 2:
The solution combines two different materials with complementary functions: a ceramic thermal barrier coating for thermal insulation and a metallic reflective layer for radiation reflection. This composite structure leverages the strengths of both materials - the ceramic's low thermal conductivity and the metal's high reflectivity - to simultaneously address both conduction and radiation heat transfer mechanisms.
2Loss of energy
If the ceramic coating is made translucent to allow heat radiation passage, then radiation heat transfer is reduced, but thermal insulation effectiveness decreases
Solution Approach 1:
The thermal protection system is segmented into two distinct functional layers: the ceramic thermal barrier coating that handles conduction insulation and the metallic reflective layer that handles radiation reflection. This segmentation allows each layer to optimize its specific function without compromising the other, avoiding the need to make the ceramic coating translucent which would reduce its insulating effectiveness.
3Loss of energy
If a reflective layer is applied to reduce radiation heat transfer, then energy loss is reduced, but coating complexity and manufacturing difficulty increase
Solution Approach 1:
The reflective layer is applied as a thin film that conforms to the underlying ceramic coating topology, including its porous microstructure. This thin film approach adds minimal complexity while effectively reducing radiation heat transfer. The conformal nature of the thin film allows it to integrate with the existing coating structure rather than requiring a completely new complex system.
4Loss of energy
If the reflective layer penetrates deeply into the porous microstructure, then radiation heat transfer is better blocked, but risk of substrate contact and potential damage increases
Solution Approach 1:
The reflective layer penetrates partially into the porous microstructure of the ceramic coating, reaching sufficient depth to effectively block radiation heat transfer pathways without exceeding the point where it would contact the substrate. This partial penetration approach provides adequate radiation blocking while maintaining a safety margin to preserve coating integrity and prevent substrate damage.
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 reduces radiation heat transfer, maintaining the durability and functionality of the thermal barrier coating while keeping the substrate cooler, thus enhancing the operational efficiency and longevity of gas turbine engine components.
Implementation Method 1
heat transport through typical ceramic thermal barrier coatings occur via conduction and radiation. Whereas the conduction of heat through these materials via phonon transport remains quite low over a wide range of temperature, the translucent nature of ceramic materials can allow for significant levels of heat transfer via radiation as the temperature increases.
Implementation Method 2
applying a conforming reflective layer to the thermal barrier material... to reduce radiation heat transport
Implementation Method 3
applying the platinum group metals via atomic layer deposition
Implementation Method 4
applying a thermal barrier material via electron beam physical vapor deposition
Data Source
AI summary
A process for coating a component includes applying a bond coat on a substrate of a component; applying a thermal barrier material to the bond coat; and applying a conforming reflective layer to the thermal barrier material, the conforming reflective layer conforming to porous microstructure of the ceramic coating.