Thermal Barrier Coating with Didymium Oxide for Molten Silicate Resistance
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Solution Overview
Problem
Existing thermal barrier coatings for gas turbine engines face challenges in resisting molten silicate, CMAS, and other salts, which can lead to degradation and reduced durability.
Innovation Solution
A thermal barrier coating system comprising a metallic substrate, a NiCoCrAlY bondcoat, and a thermal barrier coating that includes a combination of didymium oxide (neodymium oxide and praseodymium oxide) and zirconia, with specific concentration ranges to enhance resistance to molten silicates and other salts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermal barrier coatings (YSZ) are used, then thermal barrier effectiveness is achieved, but resistance to molten silicates and salts is insufficient
Solution Approach 1:
The patent modifies the chemical composition parameters of the thermal barrier coating by incorporating rare earth oxides (2-20 wt% La2O3, 2-20 wt% CeO2, 2-20 wt% Pr6O11, or 2-20 wt% Nd2O3) into the YSZ matrix. This compositional parameter change enhances the coating's chemical stability and resistance to molten silicate and salt attack while maintaining thermal barrier properties.
Solution Approach 2:
The patent creates a composite material system by combining YSZ with rare earth oxides to form a multi-phase ceramic coating. This composite structure provides both the thermal insulation properties of YSZ and the chemical resistance of rare earth oxides, simultaneously addressing thermal barrier effectiveness and resistance to CMAS/salt degradation.
2Reliability
If TGO layer is allowed to grow with time-at-temperature, then bondcoat oxidation protection is achieved, but interface layer thickness increases causing potential delamination
Solution Approach 1:
The patent modifies the TGO layer characteristics by changing the bondcoat composition to include reactive elements (Hf, Ta, W, Re) at controlled concentrations (0.1-5.0 wt% each). These compositional parameter changes affect the TGO growth rate and microstructure, enabling protection against oxidation while controlling interface layer thickness to prevent delamination during extended service.
Solution Approach 2:
The patent introduces reactive elements (Hf, Ta, W, Re) as intermediary components in the bondcoat that modify the TGO formation process. These elements act as mediators between the metal substrate and the ceramic TBC, controlling oxide scale growth and improving adhesion, thereby protecting the bondcoat from oxidation while preventing interface delamination.
3Productivity
If turbine operating temperature is increased, then turbine efficiency is improved, but thermal-mechanical stresses and fatigue increase
Solution Approach 1:
The patent employs a composite TBC system consisting of YSZ matrix reinforced with rare earth oxide phases. This composite material provides enhanced thermal insulation performance, allowing higher turbine operating temperatures and improved efficiency. The rare earth oxide phases also improve the coating's resistance to thermal cycling and mechanical stresses, maintaining component durability under elevated temperature conditions.
Solution Approach 2:
The patent optimizes the thickness and composition parameters of the thermal barrier coating to manage thermal stresses. By controlling TBC thickness (1-40 mils) and incorporating rare earth oxides that enhance fracture toughness and stress resistance, the coating can withstand thermal-mechanical stresses at higher operating temperatures without failing, thereby enabling improved turbine efficiency while maintaining component strength.
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 proposed coating system demonstrates improved resistance to molten silicates and other salts, leading to enhanced durability and performance of gas turbine engine components by maintaining thermal barrier effectiveness.
Implementation Method 1
yttria-stabilized zirconia (YSZ) (or gadolinia-stabilized zirconia (GSZ)) thermal barrier coating (TBC)
Implementation Method 2
Prior to and while the barrier coat layer is being deposited, a thermally grown oxide (TGO) layer (e.g., alumina) forms atop the bondcoat layer
Data Source
Figure 1~5
Figure 2~3
Figure 4
AI summary
An article (50; 100) has a metallic substrate (22), a bondcoat (30) atop the substrate, and a thermal barrier coating (28; 27, 28) atop the bondcoat. The thermal barrier coating or a layer thereof comprises didymium oxide and zirconia.