HF Etching of Environmental Barrier Coatings on 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 combustors, suffer from rapid recession due to water vapor-induced volatilization, leading to material loss and performance degradation when the environmental barrier coating is damaged.
Innovation Solution
A method involving an etchant liquid comprising hydrogen fluoride and a solvent is used to remove the environmental barrier coating, followed by the formation of a replacement coating on the exposed bondcoat, tailored to the specific chemical composition of the bondcoat and thermally grown oxide layer, if present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If environmental barrier coating is applied to protect silicon-based materials, then material loss from water vapor-induced volatilization is prevented, but the coating itself must be removed and reapplied when damaged, causing loss of time and increased maintenance complexity
Solution Approach 1:
The patent replaces mechanical removal methods (grit blasting, grinding) with a chemical etching process using HF-based solutions that selectively dissolve the bondcoat material, enabling faster and more precise removal of damaged coatings without mechanical abrasion of the substrate
Solution Approach 2:
The patent utilizes controlled chemical parameters (etchant composition, temperature, exposure time) to achieve selective removal of the bondcoat while preserving the substrate and EBC, allowing precise control over the removal process to minimize time and material loss
2Ease of manufacture
If conventional mechanical removal methods are used to remove damaged EBC, then coating removal is achieved, but the substrate surface is damaged and requires additional repair work
Solution Approach 1:
The patent replaces mechanical removal methods with a chemical etching process that selectively dissolves the bondcoat through chemical reaction, eliminating mechanical contact that would damage the substrate surface and requiring less subsequent repair work
Solution Approach 2:
The patent introduces a chemical etchant as an intermediary substance that facilitates selective removal of the bondcoat through chemical dissolution, acting as a mediator between the removal goal and the substrate protection requirement
3Productivity
If non-selective removal methods are used, then coating removal is achieved, but both the bondcoat and substrate are damaged, increasing material loss
Solution Approach 1:
The patent applies the principle of local quality by using an etchant with selective chemical affinity that reacts only with specific bondcoat materials (e.g., silicon-containing or mullite-containing bondcoats) while leaving the substrate and EBC unaffected, enabling precise localized removal without collateral damage
Solution Approach 2:
The patent controls chemical reaction parameters (etchant concentration, temperature, exposure time) to achieve selective removal of the bondcoat while preserving the substrate, preventing unnecessary material loss while maintaining removal efficiency
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 method effectively removes damaged environmental barrier coatings, restoring the substrate surface for new coatings, enhancing the durability and performance of high-temperature components by preventing material loss and maintaining operational integrity.
Implementation Method 1
the etchant liquid comprising 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
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4B
AI summary
A method is provided for removing an environmental barrier coating (108) from a coated component (100). The method may include contacting the coated component (100) with an etchant liquid (112) that comprises 5% by volume to 70% by volume of hydrogen fluoride and a solvent. The hydrogen fluoride reacts with silicon oxide in a thermally grown oxide layer (110) positioned between a bondcoat (104) and the environmental barrier coating (108) layer to thereby remove the thermally grown oxide layer (110) and the environmental barrier coating (108) from the bondcoat (104).