Gradient Alumina Coating for Gas Turbine Shroud Delamination
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Solution Overview
Problem
The existing coating methods for gas turbine shrouds face issues with delamination of top coatings due to weakened bonding between particles, leading to reduced heat resistance and adhesion, particularly when using alumina-based bond coatings with ceramics matrix composites.
Innovation Solution
A coating method involving a slurry deposition process where the proportion of coarse ceramix particles decreases towards the surface, forming a bond coating with a high proportion of coarse particles on the base material and a lower proportion on the top coating, relieving sintering shrinkage stress and enhancing particle bonding for improved heat resistance and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If coarse alumina powder is mixed with fine alumina powder to suppress sintering shrinkage, then sintering shrinkage is reduced, but bonding between particles is weakened causing top coating delamination
Solution Approach 1:
The patent applies local quality by creating a bond coating with non-uniform particle distribution, where the proportion of coarse particles decreases from the base material interface toward the top coating interface. This gradient structure allows the region near the base material to have high coarse particle content for shrinkage control, while the region near the top coating has fine particle dominance for strong bonding.
Solution Approach 2:
The patent changes the particle size distribution parameter through the thickness of the bond coating. By controlling the proportion of coarse to fine particles as a gradient parameter, the coating achieves optimal balance between shrinkage control and bonding strength at different locations.
2Ease of manufacture
If alumina coating material is thermal sprayed onto CMC base material, then bond coating is formed, but the coating may crack at use temperature due to crystallization
Solution Approach 1:
The patent changes the physical and chemical parameters of the coating material by using a controlled mixture of coarse and fine alumina particles in specific proportions. This particle size distribution control modifies the coating's crystallization behavior and stress distribution, preventing crack formation at service temperatures.
Solution Approach 2:
The patent creates a composite bond coating structure combining coarse and fine particles of alumina in a gradient distribution. This composite approach leverages the shrinkage control benefits of coarse particles while maintaining the bonding and crack resistance advantages of fine particles.
3Stress or pressure
If bond coating with high coarse particle content is used to relieve sintering stress, then sintering shrinkage stress is reduced, but bonding between particles is weakened
Solution Approach 1:
The patent resolves this contradiction by applying local quality - different regions of the bond coating have different particle compositions optimized for their specific functions. The base material interface region has high coarse particle content for stress relief, while the top coating interface region has high fine particle content for bonding strength.
Solution Approach 2:
The patent introduces a dimensional aspect to the particle distribution, creating a gradient through the thickness direction of the coating. This transforms a two-dimensional uniform composition into a three-dimensional graded structure, allowing simultaneous optimization of stress relief and bonding in different spatial regions.
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
This approach results in a coating layer with increased hardness and durability, effectively suppressing erosion and improving heat resistance and adhesion, while simplifying the coating production process and reducing costs.
Implementation Method 1
a slurry deposition step of depositing a slurry including a coarse ceramixs particle and a fine ceramixs particle on an oxide-based ceramics matrix composite such that a proportion of coarse particles decreases towards a surface of the base material
Implementation Method 2
a bond coating formation step of forming a bond coating by performing a heat treatment on the base material on which the slurry has been deposited
Implementation Method 3
a top coating formation step of forming a top coating by thermal spraying a ceramic onto the bond coating
Data Source
AI summary
A coating method includes depositing a slurry including a coarsely particulate ceramic and a finely particulate ceramic on a base material configured with an oxide-based ceramics matrix composite such that a proportion of coarse particles decreases towards a surface of the base material; forming a bond coating by performing a heat treatment on the base material on which the slurry has been deposited; and forming a top coating by thermally spraying a ceramic onto the bond coating. The oxide-based ceramics matrix composite is an alumina silica type oxide-based ceramics matrix composite. The coarsely particulate ceramic and the finely particulate ceramic are alumina-based powder.