Turbine Blade Tip Coating Clearance Control
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Solution Overview
Problem
Existing rotary seal systems for gas turbine engines fail to minimize friction between blade tips and shrouds during operation, leading to increased blade tip wear, oxidation, and reduced turbine performance due to inadequate management of rubbing friction and clearance.
Innovation Solution
A turbine blade tip and shroud clearance control coating system featuring an abrasive grit coating with cubic zirconia or hafnia particles embedded in an oxidation-resistant bond coating, paired with a nanolaminate thermal barrier coating on the shroud that is designed to be abradable, allowing for controlled friction reduction and maintaining minimal clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an abrasive tip coating is applied to the blade tip to abrade the shroud surface, then the blade tip clearance is reduced and maintained, but the rubbing friction between the blade tip and shroud increases causing bending stresses that may overload the blade
Solution Approach 1:
The invention applies different material properties to different components: the blade tip receives an abrasive coating (cubic boron nitride, cubic boron carbide, or silicon carbide particles in a metal matrix) to actively abrade the shroud, while the shroud receives an abradable coating (alumina, zirconia, or tungsten carbide particles in a metal matrix) that is softer and designed to be removed. This local differentiation of material properties enables clearance control while managing friction forces through controlled material removal rather than continuous rubbing.
Solution Approach 2:
The invention converts the harmful effect of rubbing friction into a beneficial process by designing the shroud with an abradable coating that is intentionally meant to be worn away. The friction that would otherwise cause stress and damage is instead used to gradually remove the softer shroud coating material, maintaining clearance control while reducing the mechanical load on the blade structure.
2Manufacturing precision
If a ceramic coated blade tip is used to abrade the inner surface of the shroud, then the blade tip to shroud clearance is minimized, but the friction during rubbing increases leading to potential blade failure
Solution Approach 1:
The invention creates a localized functional differentiation where the blade tip has a hard abrasive coating for material removal while the shroud has a softer abradable coating that is specifically designed to be worn. This local quality distinction ensures that the clearance control function is achieved through controlled abrasion of the shroud rather than continuous high-friction rubbing between two hard surfaces, thereby maintaining blade reliability.
Solution Approach 2:
The invention employs composite material structures: the blade tip coating consists of abrasive particles (cubic boron nitride, cubic boron carbide, or silicon carbide) embedded in a metal matrix, while the shroud coating consists of abradable particles (alumina, zirconia, or tungsten carbide) in a metal matrix. These composite structures provide the necessary mechanical properties for each component's specific function while managing the interaction between the two surfaces during operation.
3Loss of energy
If no abrasive or abradable coatings are used on the blade and shroud, then the rubbing friction is lower, but the blade tip clearance increases reducing turbine performance
Solution Approach 1:
The invention converts the potentially harmful rubbing friction into a beneficial clearance control mechanism. By designing the shroud with an abradable coating that is softer than the blade tip abrasive coating, the friction force is directed toward controlled material removal from the shroud rather than causing damage. This allows the system to tolerate and utilize the friction necessary for maintaining tight clearance while preventing blade failure.
Solution Approach 2:
The invention changes the material parameters of the shroud surface by applying a softer abradable coating compared to the harder abrasive coating on the blade tip. This parameter differentiation (hardness, wear resistance) enables the system to achieve tight clearance control through controlled material removal while managing the friction force through asymmetric material properties rather than relying on low-friction surfaces.
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 system effectively reduces rubbing friction and maintains optimal blade tip to shroud clearance, enhancing turbine performance and durability by using materials resistant to high temperatures and oxidation, thereby reducing maintenance costs and improving engine efficiency.
Implementation Method 1
a blade with a ceramic blade tip layer where the layer consists of aluminum oxide and zirconia-based oxide... a blade with an abrasive tip that is harder than an abradable inner shroud surface... grit particles comprise abrasive crystalline particles of cubic zirconia, cubic hafnia or mixtures thereof
Implementation Method 2
an oxidation resistant bond coating... wherein the grit particles comprise abrasive crystalline particles of cubic zirconia, cubic hafnia or mixtures thereof
Implementation Method 3
a nanolaminate thermal barrier coating on the inner surface of the turbine shroud, the nanolaminate thermal barrier coating comprising alternating layers of a first material with a second material, the first material comprising stabilized zirconia, hafnia or mixtures thereof
Data Source
AI summary
A turbine blade tip and shroud clearance control coating system comprising an abrasive blade tip coating and an abradable shroud coating are provided. The abrasive layer may comprise abrasive particles of cubic zirconia, cubic hafnia or mixtures thereof, and the abradable layer may be a nanolaminate thermal barrier coating that is softer than the abrasive layer. The invention further provides an alternate coating system comprising an abradable blade tip coating and an abrasive shroud coating.