Bi-layer Thermal Barrier Coating for CMAS Resistance
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Solution Overview
Problem
Conventional thermal barrier coatings (TBCs) in gas turbines are susceptible to degradation due to the infiltration of CMAS (calcia, magnesia, alumina, and silica) species, leading to premature spallation and reduced service life, especially in dusty environments, as they lack sufficient strain tolerance and scalability.
Innovation Solution
A bi-layer coating system comprising an inner layer with high thermal resistance and fracture toughness, and an outer layer resistant to CMAS infiltration, where the interface between the layers is designed to maintain a surface temperature below the CMAS melting point upon spallation, thereby extending the service life by arresting further spalling and providing continued thermal protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-rare-earth TBCs are used to resist CMAS infiltration, then CMAS resistance is improved, but fracture toughness deteriorates
Solution Approach 1:
The coating system is divided into two distinct layers: an inner layer providing fracture toughness and thermal protection, and an outer layer providing CMAS resistance. This segmentation allows each layer to be optimized for its specific function without compromising the other.
Solution Approach 2:
The invention uses a composite coating system combining two different materials with complementary properties. The inner layer uses a material optimized for toughness and thermal insulation, while the outer layer uses a material optimized for CMAS resistance, creating a composite structure that achieves both requirements.
2Temperature
If TBC thickness is increased to improve thermal protection, then thermal resistance is improved, but scalability deteriorates
Solution Approach 1:
The coating is segmented into two layers with different thickness requirements. The inner layer provides the bulk of thermal protection and can be optimized for thermal performance, while the outer layer provides CMAS resistance and can be applied at standard thicknesses, making the overall system scalable.
3Ease of manufacture
If conventional 8YSZ TBC is used, then manufacturing simplicity is maintained, but CMAS resistance deteriorates
Solution Approach 1:
The coating system separates the CMAS resistance function into a dedicated outer layer, allowing the inner layer to use conventional 8YSZ material that is easy to manufacture. This segmentation enables the use of simple, well-understood materials in the inner layer while providing enhanced protection through the outer layer.
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 bi-layer coating system effectively resists CMAS infiltration and spallation, maintaining thermal protection and extending the service life of turbine components by ensuring the remaining coating thickness provides adequate thermal insulation even after spallation, thus preventing rapid failure.
Implementation Method 1
The inner layer has, in a temperature range from about 1000 degrees Celsius to about 1200 degrees Celsius, a thermal resistance in a range from about 9×10−5 degree Kelvin per watt to about 23×10−5 degree Kelvin per watt
Implementation Method 2
The outer layer is more resistant to infiltration by nominal CMAS relative to 8 weight percent yttria-stabilized zirconia at a temperature of 1300 degrees Celsius
Implementation Method 3
These species can adhere to TBCs and damage them through the formation of various comparatively low-melting point phases collectively referred to as 'CMAS'
Data Source
AI summary
An article having a damage-tolerant thermal barrier coating includes a plurality of coating layers disposed over a substrate. The plurality of coatings comprises an inner layer and an outer layer. The outer layer is more resistant to infiltration by nominal CMAS relative to 8 weight percent yttria-stabilized zirconia at a temperature of 1300 degrees Celsius. The inner layer has, in a temperature range from about 1000 degrees Celsius to about 1200 degrees Celsius, a thermal resistance in a range from about 9.times.10.sup.-5 degree Kelvin per watt to about 23.times.10.sup.-5 degree Kelvin per watt.