Bilayer Thermal Barrier Coatings with Roughened Interfaces
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Solution Overview
Problem
Existing multilayer thermal barrier coatings face issues with low fracture toughness and weak bonding between ceramic layers, leading to delamination and reduced erosion resistance, particularly in components with complex geometries.
Innovation Solution
A bilayer ceramic coating system is developed with a partially stabilized zirconia lower coating, a segmented intermediate coating with increased roughness, and a fully stabilized zirconia upper coating, achieved through controlled spraying parameters and particle size adjustments to enhance interlocking and bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a fully stabilized zirconia upper coating is deposited on a partially stabilized zirconia lower coating, then thermal barrier performance is improved, but fracture toughness and erosion resistance deteriorate due to low fracture toughness of the fully stabilized coating
Solution Approach 1:
The patent applies different material compositions to different layers of the coating system. The lower coating uses partially stabilized zirconia (PSZ) with higher fracture toughness, while the upper coating uses fully stabilized zirconia (FSZ) with superior thermal barrier properties. This local differentiation allows each layer to optimize its specific function while working together as a integrated system.
2Reliability
If a segmented microstructure is used in the ceramic coatings, then erosion resistance is improved, but interface bonding strength deteriorates due to smooth surface and lack of mechanical interlocking
Solution Approach 1:
The patent introduces a roughening layer as an intermediate structure between the segmented lower coating and the upper coating. This roughening layer is deposited beforehand to create surface asperities and cavities that will subsequently provide mechanical interlocking for the upper coating, preventing delamination while preserving the erosion-resistant segmented microstructure.
3Strength
If intensive preheating is applied to improve wetting and spreading of particles, then interface bonding is improved, but homogeneous preheating becomes difficult for bulky components with complex geometries
Solution Approach 1:
Instead of attempting homogeneous preheating of the entire component, the patent applies localized roughening at the specific interface region where bonding is critical. This localized approach achieves the necessary surface modification for strong bonding without requiring complex preheating systems to uniformly heat entire bulky components with varying wall thicknesses.
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 improves the strength and robustness of the ceramic coating interface, enhancing thermal compliance and erosion resistance without compromising the microstructure, suitable for components with complex geometries.
Implementation Method 1
A coating is usually applied by a spray torch passing over the same surface several times by applying powder in layers
Implementation Method 2
The particles will spread evenly and fill almost all cavities and asperities improving in this manner the mechanical interlocking between the two coatings
Data Source
AI summary
A component with a ceramic coating system wherein the component includes a substrate, especially a nickel- or cobalt-based superalloy, a metallic bond coat, especially based on a NiCoCrAl composition, a ceramic coating system with an lower ceramic coating and an upper ceramic coating. An intermediate coating is located between lower coating and upper coating, providing a rougher surface which has a maximum thickness of 25% of the thickness of the lower coating or of the upper coating. The bonding capacity of a ceramic coating system is improved by adapting the coating parameters such as size of the powder and changing of the parameters of the spraying system.