Segmented Thermal Barrier Coating for Gas Turbine Blades
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Solution Overview
Problem
Gas turbine engine components face extreme heat and thermal gradients, leading to thermal-mechanical stresses and fatigue, which existing thermal barrier coatings struggle to adequately address, particularly due to the growth of the thermally grown oxide (TGO) layer and limitations in temperature reduction and durability.
Innovation Solution
A segmented thermal barrier coating system is implemented, featuring a metallic substrate with recesses coated with a splatted layer and a columnar layer in high-stress regions, and a columnar layer without a splatted layer in lower-stress regions, using materials like gadolinia-stabilized zirconia (GSZ) and yttria-stabilized zirconia (YSZ) with specific bondcoats and deposition methods to manage thermal expansion and erosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform thermal barrier coating is applied across the entire substrate surface, then the coating provides consistent thermal protection, but it cannot adequately manage differential thermal expansion and stress distribution in high-stress versus lower-stress regions
Solution Approach 1:
The coating is divided into two distinct types: a first coating applied to high-stress regions (including recesses) and a second coating applied to lower-stress regions. This segmentation allows each coating type to be optimized for its specific stress environment, with the first coating providing enhanced crack resistance in high-stress areas while the second coating provides adequate protection in lower-stress areas.
Solution Approach 2:
Different coating configurations are applied to different regions of the substrate based on local stress conditions. The first coating system includes a splatted layer and columnar layer for high-stress regions, while the second coating system uses only a columnar layer for lower-stress regions. This local quality approach ensures that each region receives the appropriate level of protection tailored to its specific operational demands.
2Duration of action of stationary object
If the TGO layer is allowed to grow with time-at-temperature and cycling, then the coating provides thermal barrier function, but the TGO interface layer thickens and reduces coating durability
Solution Approach 1:
The splatted layer in the first coating system acts as a cushioning layer that accommodates TGO growth and thermal expansion stresses before they can propagate through the entire coating system. This layer absorbs the harmful effects of TGO thickening and cyclic thermal stresses, protecting the bondcoat-substrate interface from failure and extending coating service life.
Solution Approach 2:
The splatted layer provides a more compliant, less dense structure compared to the columnar layer, allowing it to accommodate TGO growth and thermal stresses more effectively. This porous-like structure absorbs expansion stresses and prevents crack propagation, thereby mitigating the harmful effects of prolonged thermal exposure and cycling.
3Strength
If thermal barrier coatings are applied to reduce base metal temperature, then component durability improves, but the coatings increase device complexity and manufacturing difficulty
Solution Approach 1:
The coating system is segmented into two main types (first coating with splatted and columnar layers, second coating with only columnar layer) applied to different stress regions. This segmentation provides optimized protection for each region while maintaining a manageable manufacturing process through defined application zones.
Solution Approach 2:
Each region receives a coating configuration matched to its specific needs: high-stress regions get the more complex first coating system for enhanced durability, while lower-stress regions receive the simpler second coating system. This local quality approach optimizes overall component durability without unnecessarily complicating the entire coating system.
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 enhances durability and efficiency by allowing for differential thermal expansion and crack formation, reducing temperature at the base metal by up to 300°F (167°C) and improving turbine operating temperatures, while minimizing TGO growth and erosion resistance.
Implementation Method 1
yttria-stabilized zirconia (YSZ) (or gadolinia-stabilized zirconia (GSZ)) thermal barrier coating (TBC)
Implementation Method 2
a thermally grown oxide (TGO) layer (e.g., alumina) forms atop the bondcoat layer
Implementation Method 3
allowing for differential thermal expansion and crack formation
Data Source
AI summary
An article has a metallic substrate having a plurality of recesses. A first coating is at least at the recesses and has: a splatted layer; and a columnar layer atop the splatted layer. A second coating is away from the recesses and has: a columnar layer atop the substrate without an intervening splatted layer.