EBC Removal and Repair for Silicon-Based Turbine Components
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Solution Overview
Problem
Silicon-based materials used in high-temperature components of gas turbine engines, such as airfoils and combustor liners, suffer from rapid recession due to water vapor-induced volatilization, leading to material loss and reduced performance.
Innovation Solution
A method involving the use of hydrogen fluoride-based etchant liquids to selectively remove environmental barrier coatings (EBCs) from silicon-containing substrates, followed by mechanical removal of bondcoats if necessary, and subsequent reapplication of replacement coatings to restore the substrate's protective layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If environmental barrier coatings are applied to silicon-based materials, then protection against water vapor-induced volatilization is improved, but the complexity of the coating system increases
Solution Approach 1:
The coating system is divided into multiple functional layers: a silicon-containing bondcoat layer applied directly to the substrate, and an environmental barrier coating layer applied over the bondcoat. This segmentation allows each layer to perform its specific function independently, with the bondcoat providing adhesion and the EBC providing environmental protection.
Solution Approach 2:
The patent employs composite material structures where the EBC is composed of multiple layers including rare earth silicate layers, aluminosilicate layers, and hermetic layers. Each material contributes specific properties that together provide comprehensive protection against water vapor-induced volatilization while managing thermal and chemical stresses.
2Ease of repair
If existing coating systems are removed and reapplied, then repair capability is improved, but the time required for maintenance increases
Solution Approach 1:
The bondcoat layer is applied to the substrate in advance and serves as a permanent adhesive layer that remains on the substrate throughout the component's service life. This preliminary action eliminates the need to remove and reapply the bondcoat during maintenance, allowing only the EBC layer to be removed and reapplied, thereby reducing maintenance time.
Solution Approach 2:
The EBC layer is designed to be removable and replaceable while the bondcoat layer is retained on the substrate. During maintenance, the damaged EBC is discarded and a new EBC layer is applied over the existing bondcoat, recovering the protective function without the need to remove the adhesive layer.
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
Restores the integrity of silicon-containing components by preventing further material loss and maintaining performance in high-temperature environments, ensuring durability and operational efficiency.
Implementation Method 1
contacting the coated component with an etchant liquid comprising 5% by volume to 70% by volume of hydrogen fluoride and a solvent, wherein the hydrogen fluoride reacts with silicon oxide in the thermally grown oxide layer to thereby remove the thermally grown oxide layer and the environmental barrier coating from the bondcoat
Implementation Method 2
contacting the coated component with an etchant liquid, wherein the etchant liquid comprises phosphoric acid, 5% by volume to 70% by volume of hydrogen fluoride, and a solvent, wherein the phosphoric acid and the hydrogen fluoride react with the coating to weaken chemical bonds therein to form a chemically-weakened coating
Data Source
AI summary
A method is provided for removing a bondcoat and an environmental barrier coating from a coated component. The method may include contacting the coated component with an etchant liquid comprising phosphoric acid, 5% by volume to 70% by volume of hydrogen fluoride, and a solvent. The hydrogen fluoride and the phosphoric acid react with a composition in the bondcoat. The bondcoat is positioned within the coated component between a silicon-containing substrate and the environmental barrier coating, and the bondcoat comprises mullite.