Segmented Fully Stabilized Zirconia for Gas Turbine Tip Sealing
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Solution Overview
Problem
Existing abradable coatings in turbine sections, such as YSZ, lack the durability to withstand high temperatures and are easily rubbed away, posing a risk of metal degradation when exposed to high Turbine Inlet Temperatures (TIT) in modern gas turbines.
Innovation Solution
A segmented microstructure is introduced in Fully Stabilized Zirconia (FSZ) coatings to enhance toughness, forming vertical cracks that improve thermal strain capability and erosion resistance, allowing FSZ to be used as an abrasive coating on blade tips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Fully Stabilized Zirconia (FSZ) coating is used to withstand high temperatures, then temperature resistance is improved, but toughness deteriorates making the coating easily rubbed away
Solution Approach 1:
The FSZ coating is designed with a segmented microstructure consisting of multiple layers or zones with different properties. This segmentation allows the coating to maintain high temperature resistance while the segmented structure provides crack deflection paths that improve overall toughness and prevent catastrophic failure during rubbing contact
Solution Approach 2:
The coating system uses composite material architecture where FSZ is combined with other materials or structured as a composite system (e.g., FSZ overlay on a different substrate or combined with interlayers). This composite approach enables the system to exhibit both the high temperature stability of FSZ and enhanced toughness through the synergistic properties of the composite structure
2Ease of operation
If high porosity ceramic coating is used to improve abradability, then abradability is improved, but structural integrity deteriorates at high temperatures
Solution Approach 1:
The coating system applies different porosity levels to different locations or layers. The abradable coating layer in contact with blade tips has high porosity for good abradability, while underlying layers or the substrate interface have lower porosity to maintain structural integrity and prevent metal exposure at high temperatures
Solution Approach 2:
The coating is divided into multiple layers with progressively different porosity characteristics. The outermost layer has high porosity for abradability, while inner layers have reduced porosity to provide structural support and thermal protection, creating a gradient structure that balances both requirements
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 segmented FSZ coating significantly enhances toughness, ensuring the abradable coating is rubbed away instead of the underlying metal, providing protection and maintaining structural integrity at high temperatures.
Implementation Method 1
The coating is deposited so dense that vertical cracks are formed in it. It is well documented that the segmented microstructure combines good thermal strain capability along with significantly improved toughness and erosion resistance
Implementation Method 2
The significantly improved toughness of the segmented FSZ will ensure that the abradable will be rubbed away and not the opposite
Data Source
AI summary
A seal system for gas turbine that includes a stator and a blade with a blade tip facing the stator. The blade has a protective ceramic coating having an inner ceramic layer being made of a partially stabilized zirconia and having at least a partially segmented microstructure in form of vertical cracks. The ceramic coating further includes an outer ceramic layer made of fully stabilized zirconia and having a segmented microstructure. Advantageously, the entire airfoil surface is provided with the protective ceramic coating. With the fully stabilized zirconia coating on the tip of a blade which faces a casing with a ceramic coating, a result is a better sealing system. The stator includes an abradable coating having at least an outer ceramic coating being made of fully stabilized or ytterbium stabilized zirconia.